Publications by Department of Mesoscopic Physics
Departments of ISQI | Publications of ISQI
2023 |
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| 41. | Anand Manaparambil, Ireneusz Weymann Giant tunnel magnetoresistance induced by thermal bias Journal of Magnetism and Magnetic Materials, 587 , pp. 171272, 2023. @article{Manaparambil2023b, title = {Giant tunnel magnetoresistance induced by thermal bias}, author = {Anand Manaparambil and Ireneusz Weymann}, url = {https://www.sciencedirect.com/science/article/pii/S0304885323009228}, doi = {10.1016/j.jmmm.2023.171272}, year = {2023}, date = {2023-12-01}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {587}, pages = {171272}, abstract = {We analyze the spin-resolved transport and, in particular, the tunnel magnetoresistance of an asymmetric ferromagnetic tunnel junction with an embedded quantum dot or molecule subject to thermal and voltage bias in the nonlinear response regime. We demonstrate that such system exhibits a giant tunnel magnetoresistance effect that can be tuned by gate and bias voltages. Large values of magnetoresistance are associated with the interplay between the Kondo correlations and the ferromagnetic-contact-induced exchange field. In particular, we show that the nonequilibrium current in the parallel and antiparallel magnetic configuration of the system changes sign at different values of the voltage and thermal bias. This gives rise to giant values of magnetoresistance, the sign of which can be controlled by the applied sources.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We analyze the spin-resolved transport and, in particular, the tunnel magnetoresistance of an asymmetric ferromagnetic tunnel junction with an embedded quantum dot or molecule subject to thermal and voltage bias in the nonlinear response regime. We demonstrate that such system exhibits a giant tunnel magnetoresistance effect that can be tuned by gate and bias voltages. Large values of magnetoresistance are associated with the interplay between the Kondo correlations and the ferromagnetic-contact-induced exchange field. In particular, we show that the nonequilibrium current in the parallel and antiparallel magnetic configuration of the system changes sign at different values of the voltage and thermal bias. This gives rise to giant values of magnetoresistance, the sign of which can be controlled by the applied sources. |
| 40. | Kacper Wrześniewski, Tomasz Ślusarski, Ireneusz Weymann Nonmonotonic buildup of spin-singlet correlations in a double quantum dot Physical Review B, 108 , pp. 144307, 2023. @article{Wrześniewski2023b, title = {Nonmonotonic buildup of spin-singlet correlations in a double quantum dot}, author = {Kacper Wrześniewski and Tomasz Ślusarski and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.108.144307}, doi = {10.1103/PhysRevB.108.144307}, year = {2023}, date = {2023-10-27}, journal = {Physical Review B}, volume = {108}, pages = {144307}, abstract = {Dynamical buildup of spin-singlet correlations between the two quantum dots is investigated by means of the time-dependent numerical renormalization group method. By calculating the time evolution of the spin-spin expectation value upon a quench in the hopping between the quantum dots, we examine the timescales associated with the development of an entangled spin-singlet state in the system. Interestingly, we predict a nonmonotonic buildup of entanglement between the two dots. In particular, we find that in short timescales the effective exchange interaction between the quantum dots is of ferromagnetic type, favoring spin-triplet correlations, as opposed to the long-time limit, when strong antiferromagnetic correlations develop and eventually an entangled spin-singlet state is formed between the dots. We also numerically determine the relevant timescales and show that the physics is generally governed by the interplay between the Kondo correlations on each dot and exchange interaction between the spins of both quantum dots.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dynamical buildup of spin-singlet correlations between the two quantum dots is investigated by means of the time-dependent numerical renormalization group method. By calculating the time evolution of the spin-spin expectation value upon a quench in the hopping between the quantum dots, we examine the timescales associated with the development of an entangled spin-singlet state in the system. Interestingly, we predict a nonmonotonic buildup of entanglement between the two dots. In particular, we find that in short timescales the effective exchange interaction between the quantum dots is of ferromagnetic type, favoring spin-triplet correlations, as opposed to the long-time limit, when strong antiferromagnetic correlations develop and eventually an entangled spin-singlet state is formed between the dots. We also numerically determine the relevant timescales and show that the physics is generally governed by the interplay between the Kondo correlations on each dot and exchange interaction between the spins of both quantum dots. |
| 39. | Alexandre Huguet, Kacper Wrześniewski, Ireneusz Weymann Spin effects on transport and zero-bias anomaly in a hybrid Majorana wire-quantum dot system Scientific Reports, 13 , pp. 17279, 2023, ISSN: 2045-2322. @article{Huguet2023, title = {Spin effects on transport and zero-bias anomaly in a hybrid Majorana wire-quantum dot system}, author = {Alexandre Huguet and Kacper Wrześniewski and Ireneusz Weymann }, url = {https://www.nature.com/articles/s41598-023-44254-9}, doi = {10.1038/s41598-023-44254-9}, issn = {2045-2322}, year = {2023}, date = {2023-10-12}, journal = {Scientific Reports}, volume = {13}, pages = {17279}, abstract = {We examine the impact of spin effects on the nonequilibrium transport properties of a nanowire hosting Majorana zero-energy modes at its ends, coupled to a quantum dot junction with ferromagnetic leads. Using the real-time diagrammatic technique, we determine the current, differential conductance and current cross-correlations in the nonlinear response regime. We also explore transport in different magnetic configurations of the system, which can be quantified by the tunnel magnetoresistance. We show that the presence of Majorana quasiparticles gives rise to unique features in all spin-resolved transport characteristics, in particular, to zero-bias anomaly, negative differential conductance, negative tunnel magnetoresistance, and it is also reflected in the current cross-correlations. Moreover, we study the dependence of the zero-bias anomaly on various system parameters and demonstrate its dependence on the magnetic configuration of the system as well as on the degree of spin polarization in the leads. A highly nontrivial behavior is also found for the tunnel magnetoresistance, which exhibits regions of enhanced or negative values—new features resulting from the coupling to Majorana wire.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We examine the impact of spin effects on the nonequilibrium transport properties of a nanowire hosting Majorana zero-energy modes at its ends, coupled to a quantum dot junction with ferromagnetic leads. Using the real-time diagrammatic technique, we determine the current, differential conductance and current cross-correlations in the nonlinear response regime. We also explore transport in different magnetic configurations of the system, which can be quantified by the tunnel magnetoresistance. We show that the presence of Majorana quasiparticles gives rise to unique features in all spin-resolved transport characteristics, in particular, to zero-bias anomaly, negative differential conductance, negative tunnel magnetoresistance, and it is also reflected in the current cross-correlations. Moreover, we study the dependence of the zero-bias anomaly on various system parameters and demonstrate its dependence on the magnetic configuration of the system as well as on the degree of spin polarization in the leads. A highly nontrivial behavior is also found for the tunnel magnetoresistance, which exhibits regions of enhanced or negative values—new features resulting from the coupling to Majorana wire. |
| 38. | Kacper Wrześniewski Dynamics of Superconducting Correlations Induced by Hopping in Serial Double Quantum Dot System Acta Physica Polonica A, 143 (2), pp. 160, 2023. @article{Wrześniewski2023, title = {Dynamics of Superconducting Correlations Induced by Hopping in Serial Double Quantum Dot System}, author = {Kacper Wrześniewski}, url = {http://przyrbwn.icm.edu.pl/APP/apphome.html}, doi = {10.12693/APhysPolA.143.160}, year = {2023}, date = {2023-02-27}, journal = {Acta Physica Polonica A}, volume = {143}, number = {2}, pages = {160}, abstract = {We study the quench dynamics of superconducting pairing correlations in the double quantum dotsystem coupled to superconducting and normal metallic electrodes. The quantum dots are initiallyisolated from each other, and the subsequent dynamics are induced by the sudden switching on hoppingbetween them. We focus on the time-dependence of the real and imaginary parts of dots pairing potentialand the role of the hopping amplitude and on-site Coulomb correlations. For relatively small hoppingvalues, the evolution of the pairing potential is suppressed due to a strong single-occupation blockade.As the hopping amplitude increases, the pairing potential is dynamically redistributed between thedots and can eventually assume values of opposite signs. This effect is enhanced by the presence ofstrong on-site Coulomb interactions. The discussed numerical results are obtained by means of thetime-dependent numerical renormalization group approach.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the quench dynamics of superconducting pairing correlations in the double quantum dotsystem coupled to superconducting and normal metallic electrodes. The quantum dots are initiallyisolated from each other, and the subsequent dynamics are induced by the sudden switching on hoppingbetween them. We focus on the time-dependence of the real and imaginary parts of dots pairing potentialand the role of the hopping amplitude and on-site Coulomb correlations. For relatively small hoppingvalues, the evolution of the pairing potential is suppressed due to a strong single-occupation blockade.As the hopping amplitude increases, the pairing potential is dynamically redistributed between thedots and can eventually assume values of opposite signs. This effect is enhanced by the presence ofstrong on-site Coulomb interactions. The discussed numerical results are obtained by means of thetime-dependent numerical renormalization group approach. |
| 37. | Krzysztof Paweł Wójcik, Piotr Majek Majorana Coupling and Kondo Screening of Localized Spins Acta Physica Polonica A, 143 (2), pp. 207, 2023. @article{Wójcik2023, title = {Majorana Coupling and Kondo Screening of Localized Spins}, author = {Krzysztof Paweł Wójcik and Piotr Majek}, url = {http://przyrbwn.icm.edu.pl/APP/PDF/143/app143z2p15.pdf}, doi = {10.12693/APhysPolA.143.207}, year = {2023}, date = {2023-02-27}, journal = {Acta Physica Polonica A}, volume = {143}, number = {2}, pages = {207}, abstract = {We perform a theoretical analysis of the fate of the local magnetic moment of a quantum dot coupled to a normal metallic lead and a topological superconducting wire hosting Majorana modes at the ends. By means of simple analytical tools and numerical renormalization group calculations, we show that the proximity of the Majorana mode reduces the magnetic moment from 1/4, characteristic of a free spin 1/2, to 1/16. Coupling to the normal lead then causes the Kondo effect, such that the magnetic moment is fully screened below the Kondo temperature. The latter is vastly increased for strong coupling to Majorana mode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We perform a theoretical analysis of the fate of the local magnetic moment of a quantum dot coupled to a normal metallic lead and a topological superconducting wire hosting Majorana modes at the ends. By means of simple analytical tools and numerical renormalization group calculations, we show that the proximity of the Majorana mode reduces the magnetic moment from 1/4, characteristic of a free spin 1/2, to 1/16. Coupling to the normal lead then causes the Kondo effect, such that the magnetic moment is fully screened below the Kondo temperature. The latter is vastly increased for strong coupling to Majorana mode. |
| 36. | Anand Manaparambil, Ireneusz Weymann Nonequilibrium Seebeck effect and thermoelectric efficiency of Kondo-correlated molecular junctions Phys. Rev. B, 107 , pp. 085404, 2023. @article{Manaparambil2023, title = {Nonequilibrium Seebeck effect and thermoelectric efficiency of Kondo-correlated molecular junctions}, author = {Anand Manaparambil and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.107.085404}, doi = {10.1103/PhysRevB.107.085404}, year = {2023}, date = {2023-02-07}, journal = {Phys. Rev. B}, volume = {107}, pages = {085404}, abstract = {We theoretically study the nonequilibrium thermoelectric transport properties of a strongly-correlated molecule (or quantum dot) embedded in a tunnel junction. Assuming that the coupling of the molecule to the contacts is asymmetric, we determine the nonlinear current driven by the voltage and temperature gradients by using the perturbation theory. However, the subsystem consisting of the molecule strongly coupled to one of the contacts is solved by using the numerical renormalization group method, which allows for accurate description of Kondo correlations. We study the temperature gradient and voltage dependence of the nonlinear and differential Seebeck coefficients for various initial configurations of the system. In particular, we show that in the Coulomb blockade regime with singly occupied molecule, both thermopowers exhibit sign changes due to the Kondo correlations at nonequilibrium conditions. Moreover, we determine the nonlinear heat current and thermoelectric efficiency, demonstrating that the system can work as a heat engine with considerable efficiency, depending on the transport regime.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We theoretically study the nonequilibrium thermoelectric transport properties of a strongly-correlated molecule (or quantum dot) embedded in a tunnel junction. Assuming that the coupling of the molecule to the contacts is asymmetric, we determine the nonlinear current driven by the voltage and temperature gradients by using the perturbation theory. However, the subsystem consisting of the molecule strongly coupled to one of the contacts is solved by using the numerical renormalization group method, which allows for accurate description of Kondo correlations. We study the temperature gradient and voltage dependence of the nonlinear and differential Seebeck coefficients for various initial configurations of the system. In particular, we show that in the Coulomb blockade regime with singly occupied molecule, both thermopowers exhibit sign changes due to the Kondo correlations at nonequilibrium conditions. Moreover, we determine the nonlinear heat current and thermoelectric efficiency, demonstrating that the system can work as a heat engine with considerable efficiency, depending on the transport regime. |
2022 |
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| 35. | Irina Werner, Jan Griebel, Albert Masip-Sánchez, Xavier López, Karol Załęski, Piotr Kozłowski, Axel Kahnt, Martin Boerner, Ziyan Warneke, Jonas Warneke, Kirill Yu. Monakhov Inorganic Chemistry, 62 (9), pp. 3761-3775, 2022, (PMID: 36534941). @article{doi:10.1021/acs.inorgchem.2c03599, title = {Hybrid Molecular Magnets with Lanthanide- and Countercation-Mediated Interfacial Electron Transfer between Phthalocyanine and Polyoxovanadate}, author = {Irina Werner and Jan Griebel and Albert Masip-Sánchez and Xavier López and Karol Załęski and Piotr Kozłowski and Axel Kahnt and Martin Boerner and Ziyan Warneke and Jonas Warneke and Kirill Yu. Monakhov}, url = {https://doi.org/10.1021/acs.inorgchem.2c03599}, doi = {10.1021/acs.inorgchem.2c03599}, year = {2022}, date = {2022-12-19}, journal = {Inorganic Chemistry}, volume = {62}, number = {9}, pages = {3761-3775}, note = {PMID: 36534941}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
| 34. | Piotr Majek, Grzegorz Górski, Tadeusz Domański, Ireneusz Weymann Hallmarks of Majorana mode leaking into a hybrid double quantum dot Phys. Rev. B, 106 , pp. 155123, 2022. @article{Majek2022c, title = {Hallmarks of Majorana mode leaking into a hybrid double quantum dot}, author = {Piotr Majek and Grzegorz Górski and Tadeusz Domański and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.155123}, doi = {10.1103/PhysRevB.106.155123}, year = {2022}, date = {2022-10-13}, journal = {Phys. Rev. B}, volume = {106}, pages = {155123}, abstract = {We investigate the spectral and transport properties of a double quantum dot laterally attached to a topological superconducting nanowire, hosting the Majorana zero-energy modes. Specifically, we consider a geometry, in which the outer quantum dot is embedded between the external normal and superconducting leads, forming a circuit. First, we derive analytical expressions for the bound states in the case of an uncorrelated system and discuss their signatures in the tunneling spectroscopy. Then, we explore the case of strongly correlated quantum dots by performing the numerical renormalization group calculations, focusing on the interplay and relationship between the leaking Majorana mode and the Kondo states on both quantum dots. Finally, we discuss feasible means to experimentally probe the in-gap quasiparticles by using the Andreev spectroscopy based on the particle-to-hole scattering mechanism.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate the spectral and transport properties of a double quantum dot laterally attached to a topological superconducting nanowire, hosting the Majorana zero-energy modes. Specifically, we consider a geometry, in which the outer quantum dot is embedded between the external normal and superconducting leads, forming a circuit. First, we derive analytical expressions for the bound states in the case of an uncorrelated system and discuss their signatures in the tunneling spectroscopy. Then, we explore the case of strongly correlated quantum dots by performing the numerical renormalization group calculations, focusing on the interplay and relationship between the leaking Majorana mode and the Kondo states on both quantum dots. Finally, we discuss feasible means to experimentally probe the in-gap quasiparticles by using the Andreev spectroscopy based on the particle-to-hole scattering mechanism. |
| 33. | X.-G. Wang, L. Chotorlishvili, G. Tatara, Anna Dyrdał, Guang-hua Guo, V. K. Dugaev, Józef Barnaś, S.S.P. Parkin, A. Ernst Skyrmion lattice hosted in synthetic antiferromagnets and helix modes Phys. Rev. B, 106 , pp. 104424, 2022. @article{Wang2022b, title = {Skyrmion lattice hosted in synthetic antiferromagnets and helix modes}, author = {X.-G. Wang and L. Chotorlishvili and G. Tatara and Anna Dyrdał and Guang-hua Guo and V. K. Dugaev and Józef Barnaś and S.S.P. Parkin and A. Ernst}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.104424}, doi = {10.1103/PhysRevB.106.104424}, year = {2022}, date = {2022-09-20}, journal = {Phys. Rev. B}, volume = {106}, pages = {104424}, abstract = {Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we have constructed an analytical model based on three coupled helices and found a linear gapless mode. Micromagnetic simulations also support this result. Moreover, a similar result has been achieved within the rigid skyrmion lattice model based on the coupled Thiele's equations, when the coupling between skyrmions in different layers of the synthetic antiferromagnetic is comparable to or larger than the intralayer coupling. In addition, we also consider the orbital angular momentum and spin pumping current associated with phason excitations. Due to the gapless excitations in the case of skyrmion lattice, the pumping current is nonzero for the arbitrary frequency of pumping microwaves. In the case of individual skyrmions, no current is pumped when microwave frequency is inside the gap of the spectrum of individual skyrmions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we have constructed an analytical model based on three coupled helices and found a linear gapless mode. Micromagnetic simulations also support this result. Moreover, a similar result has been achieved within the rigid skyrmion lattice model based on the coupled Thiele's equations, when the coupling between skyrmions in different layers of the synthetic antiferromagnetic is comparable to or larger than the intralayer coupling. In addition, we also consider the orbital angular momentum and spin pumping current associated with phason excitations. Due to the gapless excitations in the case of skyrmion lattice, the pumping current is nonzero for the arbitrary frequency of pumping microwaves. In the case of individual skyrmions, no current is pumped when microwave frequency is inside the gap of the spectrum of individual skyrmions. |
| 32. | X.-G. Wang, Guang-hua Guo, Anna Dyrdał, Józef Barnaś, V. K. Dugaev, S. S. P. Parkin, A. Ernst, L. Chotorlishvili Skyrmion Echo in a System of Interacting Skyrmions Phys. Rev. Lett., 129 , pp. 126101, 2022. @article{Wang2022, title = {Skyrmion Echo in a System of Interacting Skyrmions}, author = {X.-G. Wang and Guang-hua Guo and Anna Dyrdał and Józef Barnaś and V. K. Dugaev and S. S. P. Parkin and A. Ernst and L. Chotorlishvili}, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.126101}, doi = {10.1103/PhysRevLett.129.126101}, year = {2022}, date = {2022-09-14}, journal = {Phys. Rev. Lett.}, volume = {129}, pages = {126101}, abstract = {We consider helical rotation of skyrmions confined in the potentials formed by nanodisks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Because of the distortion of the lattice, impurities, or pinning effect, confined skyrmions experience slightly different local fields, which leads to dephasing of the initial signal. The interaction between skyrmions also can contribute to the dephasing process. However, switching the magnetization direction in the nanodiscs (e.g., by spin transfer torque) also switches the helical rotation of the skyrmions from clockwise to anticlockwise (or vice versa), and this restores the initial signal (which is the essence of skyrmion echo).}, keywords = {}, pubstate = {published}, tppubtype = {article} } We consider helical rotation of skyrmions confined in the potentials formed by nanodisks. Based on numerical and analytical calculations we propose the skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation is also proposed. Because of the distortion of the lattice, impurities, or pinning effect, confined skyrmions experience slightly different local fields, which leads to dephasing of the initial signal. The interaction between skyrmions also can contribute to the dephasing process. However, switching the magnetization direction in the nanodiscs (e.g., by spin transfer torque) also switches the helical rotation of the skyrmions from clockwise to anticlockwise (or vice versa), and this restores the initial signal (which is the essence of skyrmion echo). |
| 31. | Anand Manaparambil, Andreas Weichselbaum, Jan von Delft, Ireneusz Weymann Nonequilibrium spintronic transport through Kondo impurities Phys. Rev. B, 106 , pp. 125413, 2022. @article{Manaparambil2022, title = {Nonequilibrium spintronic transport through Kondo impurities}, author = {Anand Manaparambil and Andreas Weichselbaum and Jan von Delft and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.125413}, doi = {10.1103/PhysRevB.106.125413}, year = {2022}, date = {2022-09-14}, journal = {Phys. Rev. B}, volume = {106}, pages = {125413}, abstract = {In this work we analyze the nonequilibrium transport through a quantum impurity (quantum dot or molecule) attached to ferromagnetic leads by using a hybrid numerical renormalization group–time-dependent density matrix renormalization group thermofield quench approach. For this, we study the bias dependence of the differential conductance through the system, which shows a finite zero-bias peak, characteristic of the Kondo resonance and reminiscent of the equilibrium local density of states. In the nonequilibrium settings, the resonance in the differential conductance is also found to decrease with increasing the lead spin polarization. The latter induces an effective exchange field that lifts the spin degeneracy of the dot level. Therefore, as we demonstrate, the Kondo resonance can be restored by counteracting the exchange field with a finite external magnetic field applied to the system. Finally, we investigate the influence of temperature on the nonequilibrium conductance, focusing on the split Kondo resonance. Our work thus provides an accurate quantitative description of the spin-resolved transport properties relevant for quantum dots and molecules embedded in magnetic tunnel junctions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this work we analyze the nonequilibrium transport through a quantum impurity (quantum dot or molecule) attached to ferromagnetic leads by using a hybrid numerical renormalization group–time-dependent density matrix renormalization group thermofield quench approach. For this, we study the bias dependence of the differential conductance through the system, which shows a finite zero-bias peak, characteristic of the Kondo resonance and reminiscent of the equilibrium local density of states. In the nonequilibrium settings, the resonance in the differential conductance is also found to decrease with increasing the lead spin polarization. The latter induces an effective exchange field that lifts the spin degeneracy of the dot level. Therefore, as we demonstrate, the Kondo resonance can be restored by counteracting the exchange field with a finite external magnetic field applied to the system. Finally, we investigate the influence of temperature on the nonequilibrium conductance, focusing on the split Kondo resonance. Our work thus provides an accurate quantitative description of the spin-resolved transport properties relevant for quantum dots and molecules embedded in magnetic tunnel junctions. |
| 30. | L. Chotorlishvili, Xi-guang Wang, Anna Dyrdał, Guang-hua Guo, Vitalii K. Dugaev, Józef Barnaś, J. Berakdar Rectification of the spin Seebeck current in noncollinear antiferromagnets Phys. Rev. B, 106 (1), pp. 014417, 2022, ISSN: 2469-9969. @article{Chotorlishvili2022, title = {Rectification of the spin Seebeck current in noncollinear antiferromagnets}, author = {L. Chotorlishvili and Xi-guang Wang and Anna Dyrdał and Guang-hua Guo and Vitalii K. Dugaev and Józef Barnaś and J. Berakdar}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.014417}, doi = {10.1103/PhysRevB.106.014417}, issn = {2469-9969}, year = {2022}, date = {2022-07-25}, journal = {Phys. Rev. B}, volume = {106}, number = {1}, pages = {014417}, abstract = {In the absence of an external magnetic field and a spin-polarized charge current, an antiferromagnetic system supports two degenerate magnon modes. An applied thermal bias activates the magnetic dynamics, leading to a magnon flow from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate bands contribute to the magnon current but the orientations of the magnetic moments underlying the magnons are opposite in different bands. Therefore, while the magnon current is nonzero, the net spin current is zero. To obtain a nonzero net spin current, one needs to apply either a magnetic field or a spin-polarized charge current that lifts the bands' degeneracy. Here, attaching a thermal contact to one edge of a helical nanowire, we study three different magnonic spin currents: (i) the exchange, and (ii) Dzyaloshinskii–Moriya spin currents flowing along the helical nanowire, and (iii) magnonic spin current pumped into the adjacent normal-metal layer. We find that the combination of Dzyaloshinskii–Moriya interaction and external magnetic field substantially enhances the spin current compared to the current generated solely through a magnetic field. Due to nonreciprocal magnons and magnon dichroism effect, the Dzyaloshinskii–Moriya and exchange spin currents show left-right propagation asymmetry, with 20% of current rectification. The spin pumping current shows a slight asymmetry only in the case of a strong Dzyaloshinskii–Moriya interaction. The observed effects are explained in terms of the magnon dispersion relations and the magnon Doppler effect.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In the absence of an external magnetic field and a spin-polarized charge current, an antiferromagnetic system supports two degenerate magnon modes. An applied thermal bias activates the magnetic dynamics, leading to a magnon flow from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate bands contribute to the magnon current but the orientations of the magnetic moments underlying the magnons are opposite in different bands. Therefore, while the magnon current is nonzero, the net spin current is zero. To obtain a nonzero net spin current, one needs to apply either a magnetic field or a spin-polarized charge current that lifts the bands' degeneracy. Here, attaching a thermal contact to one edge of a helical nanowire, we study three different magnonic spin currents: (i) the exchange, and (ii) Dzyaloshinskii–Moriya spin currents flowing along the helical nanowire, and (iii) magnonic spin current pumped into the adjacent normal-metal layer. We find that the combination of Dzyaloshinskii–Moriya interaction and external magnetic field substantially enhances the spin current compared to the current generated solely through a magnetic field. Due to nonreciprocal magnons and magnon dichroism effect, the Dzyaloshinskii–Moriya and exchange spin currents show left-right propagation asymmetry, with 20% of current rectification. The spin pumping current shows a slight asymmetry only in the case of a strong Dzyaloshinskii–Moriya interaction. The observed effects are explained in terms of the magnon dispersion relations and the magnon Doppler effect. |
| 29. | Mir Ali Jafari, A. A. Kordbacheh, Anna Dyrdał J. Magn. Magn. Mater., 554 , pp. 169260, 2022, ISSN: 0304-8853. @article{Jafari2022b, title = {Electronic and magnetic properties of silicene monolayer under bi-axial mechanical strain: First principles study}, author = {Mir Ali Jafari and A. A. Kordbacheh and Anna Dyrdał}, url = {https://www.sciencedirect.com/science/article/pii/S0304885322002116?via%3Dihub}, doi = {10.1016/j.jmmm.2022.169260}, issn = {0304-8853}, year = {2022}, date = {2022-07-15}, journal = {J. Magn. Magn. Mater.}, volume = {554}, pages = {169260}, abstract = {Mechanical control of electronic and magnetic properties of 2D Van-der-Waals heterostructures gives new possibilities for further development of spintronics and information-related technologies. Using the density functional theory, we investigate the structural, electronic and magnetic properties of silicene monolayer with substituted Chromium atoms and under a small biaxial strain (-6% < e < 8%). Our results indicate that the Cr-doped silicene nanosheets without strain have magnetic metallic, half-metallic or semiconducting properties depending on the type of substitution. We also show that the magnetic moments associated with the monomer and vertical dimer substitutions change very weakly with strain. However, the magnetic moment associated with the horizontal dimer substitution decreases when either compressive or tensile strain is applied to the system. Additionally, we show that the largest semiconductor band-gap is approximately 0.13 eV under zero strain for the vertical Cr-doped silicene. Finally, biaxial compressive strain leads to irregular changes in the magnetic moment for Cr vertical dimer substitution.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mechanical control of electronic and magnetic properties of 2D Van-der-Waals heterostructures gives new possibilities for further development of spintronics and information-related technologies. Using the density functional theory, we investigate the structural, electronic and magnetic properties of silicene monolayer with substituted Chromium atoms and under a small biaxial strain (-6% < e < 8%). Our results indicate that the Cr-doped silicene nanosheets without strain have magnetic metallic, half-metallic or semiconducting properties depending on the type of substitution. We also show that the magnetic moments associated with the monomer and vertical dimer substitutions change very weakly with strain. However, the magnetic moment associated with the horizontal dimer substitution decreases when either compressive or tensile strain is applied to the system. Additionally, we show that the largest semiconductor band-gap is approximately 0.13 eV under zero strain for the vertical Cr-doped silicene. Finally, biaxial compressive strain leads to irregular changes in the magnetic moment for Cr vertical dimer substitution. |
| 28. | Amir Nasser Zarezad, Anna Dyrdał Bilinear magnetoresistance in topological insulators: Role of magnetic disorder J. Magn. Magn. Mater., 552 , pp. 169167, 2022, ISSN: 0304-8853. @article{Zarezad2022, title = {Bilinear magnetoresistance in topological insulators: Role of magnetic disorder}, author = {Amir Nasser Zarezad and Anna Dyrdał}, url = {https://www.sciencedirect.com/science/article/pii/S0304885322001329?via%3Dihub}, doi = {10.1016/j.jmmm.2022.169167}, issn = {0304-8853}, year = {2022}, date = {2022-06-15}, journal = {J. Magn. Magn. Mater.}, volume = {552}, pages = {169167}, abstract = {Bilinear magnetoresistance is a nonlinear transport phenomenon that scales linearly with the electric and magnetic fields, and appears in nonmagnetic systems with strong spin–orbit coupling, such as topological insulators (TIs). Using the semiclassical Boltzmann theory and generalized relaxation time approximation, we consider in detail the bilinear magnetoresistance in an effective model describing surface states of three-dimensional topological insulators. We show that the presence of magnetic impurities remarkably modifies the BMR signal. In general, scattering on magnetic impurities reduces magnitude of BMR. Apart from this, an additional modulation of the angular dependence of BMR appears when the spin-dependent component of the impurity potential dominates the scalar one.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Bilinear magnetoresistance is a nonlinear transport phenomenon that scales linearly with the electric and magnetic fields, and appears in nonmagnetic systems with strong spin–orbit coupling, such as topological insulators (TIs). Using the semiclassical Boltzmann theory and generalized relaxation time approximation, we consider in detail the bilinear magnetoresistance in an effective model describing surface states of three-dimensional topological insulators. We show that the presence of magnetic impurities remarkably modifies the BMR signal. In general, scattering on magnetic impurities reduces magnitude of BMR. Apart from this, an additional modulation of the angular dependence of BMR appears when the spin-dependent component of the impurity potential dominates the scalar one. |
| 27. | Tomasz Ślusarski, Kacper Wrześniewski, Ireneusz Weymann Numerical renormalization group study of the Loschmidt echo in Kondo systems Scientific Reports, 12 , pp. 9799, 2022. @article{Ślusarski2022, title = {Numerical renormalization group study of the Loschmidt echo in Kondo systems}, author = {Tomasz Ślusarski and Kacper Wrześniewski and Ireneusz Weymann}, url = {https://www.nature.com/articles/s41598-022-14108-x}, doi = {10.1038/s41598-022-14108-x}, year = {2022}, date = {2022-06-13}, journal = {Scientific Reports}, volume = {12}, pages = {9799}, abstract = {We study the dynamical properties of the one-channel and two-channel spin-1/2 Kondo models after quenching in Hamiltonian variables. Eigen spectrum of the initial and final Hamiltonians is calculated by using the numerical renormalization group method implemented within the matrix product states formalism. We consider multiple quench protocols in the considered Kondo systems, also in the presence of external magnetic field of different intensities. The main emphasis is put on the analysis of the behavior of the Loschmidt echo L(t), which measures the ability of the system’s revival to its initial state after a quench. We show that the decay of the Loschmidt echo strongly depends on the type of quench and the ground state of the system. For the one-channel Kondo model, we show that L(t) decays as, L(t)∼(t⋅TK)^−1.4, where TK is the Kondo temperature, while for the two-channel Kondo model, we demonstrate that the decay is slower and given by L(t)∼(t⋅TK)^−0.7. In addition, we also determine the dynamical behavior of the impurity’s magnetization, which sheds light on identification of the relevant time scales in the system’s dynamics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the dynamical properties of the one-channel and two-channel spin-1/2 Kondo models after quenching in Hamiltonian variables. Eigen spectrum of the initial and final Hamiltonians is calculated by using the numerical renormalization group method implemented within the matrix product states formalism. We consider multiple quench protocols in the considered Kondo systems, also in the presence of external magnetic field of different intensities. The main emphasis is put on the analysis of the behavior of the Loschmidt echo L(t), which measures the ability of the system’s revival to its initial state after a quench. We show that the decay of the Loschmidt echo strongly depends on the type of quench and the ground state of the system. For the one-channel Kondo model, we show that L(t) decays as, L(t)∼(t⋅TK)^−1.4, where TK is the Kondo temperature, while for the two-channel Kondo model, we demonstrate that the decay is slower and given by L(t)∼(t⋅TK)^−0.7. In addition, we also determine the dynamical behavior of the impurity’s magnetization, which sheds light on identification of the relevant time scales in the system’s dynamics. |
| 26. | Vrishali Sonar, Rohan Dehankar, K. P. Vijayalakshmi, Natalio Mingo, Ankita Katre Site-independent strong phonon-vacancy scattering in high-temperature ceramics ZrB2 and HfB2 Phys. Rev. Materials, 6 , pp. 065403, 2022. @article{Sonar2022, title = {Site-independent strong phonon-vacancy scattering in high-temperature ceramics ZrB2 and HfB2}, author = {Vrishali Sonar and Rohan Dehankar and K. P. Vijayalakshmi and Natalio Mingo and Ankita Katre}, url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.6.065403}, doi = {10.1103/PhysRevMaterials.6.065403}, year = {2022}, date = {2022-06-10}, journal = {Phys. Rev. Materials}, volume = {6}, pages = {065403}, abstract = {Similar effects of metal and boron vacancies on phonon scattering and lattice thermal conductivity (κl) of ZrB2 and HfB2 are reported. These defects challenge the conventional understanding that associates larger impacts to bigger defects. We find the underlying reason to be a strong local perturbation caused by boron vacancy that substantially changes the interatomic force constants. In contrast, a long ranged but weaker perturbation is seen in the case of metal vacancy. We show that these behaviors originate from a mixed metallic and covalent bonding nature in the metal diborides. The thermal transport calculations are performed in a complete ab initio framework based on Boltzmann transport equation and density functional theory. Phonon-vacancy scattering is calculated using ab initio Green's function approach. Effects of natural isotopes and grain boundaries on κl are also systematically investigated, however we find an influential role of vacancies to explain large variations seen in the experiments. We further report a two-order of magnitude difference between the amorphous and pure-crystal limits. Our results outline significant material design aspects for these multifunctional high-temperature ceramics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Similar effects of metal and boron vacancies on phonon scattering and lattice thermal conductivity (κl) of ZrB2 and HfB2 are reported. These defects challenge the conventional understanding that associates larger impacts to bigger defects. We find the underlying reason to be a strong local perturbation caused by boron vacancy that substantially changes the interatomic force constants. In contrast, a long ranged but weaker perturbation is seen in the case of metal vacancy. We show that these behaviors originate from a mixed metallic and covalent bonding nature in the metal diborides. The thermal transport calculations are performed in a complete ab initio framework based on Boltzmann transport equation and density functional theory. Phonon-vacancy scattering is calculated using ab initio Green's function approach. Effects of natural isotopes and grain boundaries on κl are also systematically investigated, however we find an influential role of vacancies to explain large variations seen in the experiments. We further report a two-order of magnitude difference between the amorphous and pure-crystal limits. Our results outline significant material design aspects for these multifunctional high-temperature ceramics. |
| 25. | Piotr Majek, Ireneusz Weymann Majorana-Kondo competition in a cross-shaped double quantum dot-topological superconductor system Journal of Magnetism and Magnetic Materials, (549), pp. 168935, 2022. @article{Majek2022, title = {Majorana-Kondo competition in a cross-shaped double quantum dot-topological superconductor system}, author = {Piotr Majek and Ireneusz Weymann}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0304885321011331}, doi = {10.1016/j.jmmm.2021.168935}, year = {2022}, date = {2022-05-01}, journal = {Journal of Magnetism and Magnetic Materials}, number = {549}, pages = {168935}, abstract = {We examine the transport properties of a double quantum dot system coupled to a topological superconducting nanowire hosting Majorana quasiparticles at its ends, with the central quantum dot attached to the left and right leads. We focus on the behavior of the local density of states and the linear conductance, calculated with the aid of the numerical renormalization group method, to describe the influence of the Majorana coupling on the low-temperature transport properties induced by the Kondo correlations. In particular, we show that the presence of Majorana quasiparticles in the system affects both the spin-up and spin-down transport channels, affecting the energy scales associated with the first-stage and second-stage Kondo temperatures, respectively, and modifying the low-energy behavior of the system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We examine the transport properties of a double quantum dot system coupled to a topological superconducting nanowire hosting Majorana quasiparticles at its ends, with the central quantum dot attached to the left and right leads. We focus on the behavior of the local density of states and the linear conductance, calculated with the aid of the numerical renormalization group method, to describe the influence of the Majorana coupling on the low-temperature transport properties induced by the Kondo correlations. In particular, we show that the presence of Majorana quasiparticles in the system affects both the spin-up and spin-down transport channels, affecting the energy scales associated with the first-stage and second-stage Kondo temperatures, respectively, and modifying the low-energy behavior of the system. |
| 24. | Piotr Trocha, Emil Siuda Spin-thermoelectric effects in a quantum dot hybrid system with magnetic insulator Scientific Reports, 12 (5348), 2022. @article{Trocha2022c, title = {Spin-thermoelectric effects in a quantum dot hybrid system with magnetic insulator}, author = {Piotr Trocha and Emil Siuda}, url = {https://www.nature.com/articles/s41598-022-09105-z}, doi = {10.1038/s41598-022-09105-z}, year = {2022}, date = {2022-03-30}, journal = {Scientific Reports}, volume = {12}, number = {5348}, abstract = {We investigate spin thermoelectric properties of a hybrid system consisting of a single-level quantum dot attached to magnetic insulator and metal electrodes. Magnetic insulator is assumed to be of ferromagnetic type and is a source of magnons, whereas metallic lead is reservoir of electrons. The temperature gradient set between the magnetic insulator and metallic electrodes induces the spin current flowing through the system. The generated spin current of magnonic (electric) type is converted to electric (magnonic) spin current by means of quantum dot. Expanding spin and heat currents flowing through the system, up to linear order, we introduce basic spin thermoelectric coefficients including spin conductance, spin Seebeck and spin Peltier coefficients and heat conductance. We analyse the spin thermoelectric properties of the system in two cases: in the large ondot Coulomb repulsion limit and when these interactions are finite.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate spin thermoelectric properties of a hybrid system consisting of a single-level quantum dot attached to magnetic insulator and metal electrodes. Magnetic insulator is assumed to be of ferromagnetic type and is a source of magnons, whereas metallic lead is reservoir of electrons. The temperature gradient set between the magnetic insulator and metallic electrodes induces the spin current flowing through the system. The generated spin current of magnonic (electric) type is converted to electric (magnonic) spin current by means of quantum dot. Expanding spin and heat currents flowing through the system, up to linear order, we introduce basic spin thermoelectric coefficients including spin conductance, spin Seebeck and spin Peltier coefficients and heat conductance. We analyse the spin thermoelectric properties of the system in two cases: in the large ondot Coulomb repulsion limit and when these interactions are finite. |
| 23. | Mir Ali Jafari, Anna Dyrdał Molecules, 27 (7), pp. 2228, 2022, ISSN: 1420-3049. @article{Jafari2022c, title = {First Principle Study on Electronic and Transport Properties of Finite-Length Nanoribbons and Nanodiscs for Selected Two-Dimensional Materials}, author = {Mir Ali Jafari and Anna Dyrdał}, url = {https://www.mdpi.com/1420-3049/27/7/2228}, doi = {10.3390/molecules27072228}, issn = {1420-3049}, year = {2022}, date = {2022-03-29}, journal = {Molecules}, volume = {27}, number = {7}, pages = {2228}, abstract = {Using the density functional theory, we calculate electronic states of various nanoribbons and nanodiscs formed from selected two-dimensional materials, such as graphene, silicene, and hexagonal boron nitride. The main objective of the analysis is a search for zero-energy states in such systems, which is an important issue as their presence indicates certain topological properties associated with chirality. The analysis is also supported by calculating transport properties.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using the density functional theory, we calculate electronic states of various nanoribbons and nanodiscs formed from selected two-dimensional materials, such as graphene, silicene, and hexagonal boron nitride. The main objective of the analysis is a search for zero-energy states in such systems, which is an important issue as their presence indicates certain topological properties associated with chirality. The analysis is also supported by calculating transport properties. |
| 22. | Kacper Wrześniewski, Ireneusz Weymann, Nicholas Sedlmayr, Tadeusz Domański Dynamical quantum phase transitions in a mesoscopic superconducting system Phys. Rev. B, 105 , pp. 094514, 2022. @article{Wrześniewski2022c, title = {Dynamical quantum phase transitions in a mesoscopic superconducting system}, author = {Kacper Wrześniewski and Ireneusz Weymann and Nicholas Sedlmayr and Tadeusz Domański}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.094514}, doi = {10.1103/PhysRevB.105.094514}, year = {2022}, date = {2022-03-25}, journal = {Phys. Rev. B}, volume = {105}, pages = {094514}, abstract = {We inspect the signatures of dynamical quantum phase transitions driven by quantum quenches acting on a correlated quantum dot embedded between superconducting and metallic reservoirs. Under stationary conditions, the proximity-induced electron pairing, competing with strong Coulomb repulsion, enforces the quantum dot to be either in the singly occupied or BCS-type ground state, depending on its energy level and coupling to the superconducting lead. By means of the time-dependent numerical renormalization group approach, we study the system's time evolution upon traversing the phase boundary between these two states, examining the Loschmidt echo and revealing nonanalytic features in the low-energy return rate, which signal dynamical quantum phase transitions. We also show that these phase transitions are accompanied by the corresponding local extrema in the pairing correlation function and dot's occupation. Since the proposed quench protocols can be realized in a controllable manner, the detection of this dynamical singlet-doublet phase transition should be feasible by performing tunneling spectroscopy measurements.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We inspect the signatures of dynamical quantum phase transitions driven by quantum quenches acting on a correlated quantum dot embedded between superconducting and metallic reservoirs. Under stationary conditions, the proximity-induced electron pairing, competing with strong Coulomb repulsion, enforces the quantum dot to be either in the singly occupied or BCS-type ground state, depending on its energy level and coupling to the superconducting lead. By means of the time-dependent numerical renormalization group approach, we study the system's time evolution upon traversing the phase boundary between these two states, examining the Loschmidt echo and revealing nonanalytic features in the low-energy return rate, which signal dynamical quantum phase transitions. We also show that these phase transitions are accompanied by the corresponding local extrema in the pairing correlation function and dot's occupation. Since the proposed quench protocols can be realized in a controllable manner, the detection of this dynamical singlet-doublet phase transition should be feasible by performing tunneling spectroscopy measurements. |
| 21. | Mir Ali Jafari, Małgorzata Wawrzyniak-Adamczewska, Stefan Stagraczyński, Anna Dyrdał, Józef Barnaś Spin valve effect in two-dimensional VSe2 system J. Magn. Magn. Mater., 548 , pp. 168921, 2022, ISSN: 0304-8853. @article{Jafari2022, title = {Spin valve effect in two-dimensional VSe2 system}, author = {Mir Ali Jafari and Małgorzata Wawrzyniak-Adamczewska and Stefan Stagraczyński and Anna Dyrdał and Józef Barnaś}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321011215?via%3Dihub}, doi = {10.1016/j.jmmm.2021.168921}, issn = {0304-8853}, year = {2022}, date = {2022-03-15}, journal = {J. Magn. Magn. Mater.}, volume = {548}, pages = {168921}, abstract = {Vanadium based dichalcogenides, VSe2, are two-dimensional materials in which magnetic Vanadium atoms are arranged in a hexagonal lattice and are coupled ferromagnetically within the plane. However, adjacent atomic planes are coupled antiferromagnetically. This provides new and interesting opportunities for application in spintronics and data storage and processing technologies. A spin valve magnetoresistance may be achieved when magnetic moments of both atomic planes are driven to parallel alignment by an external magnetic field. The resistance change associated with the transition from antiparallel to parallel configuration is qualitatively similar to that observed in artificially layered metallic magnetic structures. Detailed electronic structure of VSe2 was obtained from DFT calculations. Then, the ballistic spin-valve magnetoresistance was determined within the Landauer formalism. In addition, we also analyze thermal and thermoelectric properties. Both phases of VSe2, denoted as H and T, are considered.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Vanadium based dichalcogenides, VSe2, are two-dimensional materials in which magnetic Vanadium atoms are arranged in a hexagonal lattice and are coupled ferromagnetically within the plane. However, adjacent atomic planes are coupled antiferromagnetically. This provides new and interesting opportunities for application in spintronics and data storage and processing technologies. A spin valve magnetoresistance may be achieved when magnetic moments of both atomic planes are driven to parallel alignment by an external magnetic field. The resistance change associated with the transition from antiparallel to parallel configuration is qualitatively similar to that observed in artificially layered metallic magnetic structures. Detailed electronic structure of VSe2 was obtained from DFT calculations. Then, the ballistic spin-valve magnetoresistance was determined within the Landauer formalism. In addition, we also analyze thermal and thermoelectric properties. Both phases of VSe2, denoted as H and T, are considered. |
| 20. | Patrycja Tulewicz, Kacper Wrześniewski, Ireneusz Weymann Spintronic transport through a double quantum dot-based spin valve with noncollinear magnetizations Journal of Magnetism and Magnetic Materials, 546 , pp. 168788, 2022. @article{Tulewicz2022, title = {Spintronic transport through a double quantum dot-based spin valve with noncollinear magnetizations}, author = {Patrycja Tulewicz and Kacper Wrześniewski and Ireneusz Weymann}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321010118}, doi = {10.1016/j.jmmm.2021.168788}, year = {2022}, date = {2022-03-15}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {546}, pages = {168788}, abstract = {We study the magnetoresistive properties of a spin valve based on a double quantum dot attached to ferromagnetic leads with noncollinear alignment of magnetic moments. It is assumed that each dot is strongly coupled to its own ferromagnetic electrode, while the hopping between the dots is relatively weak. The calculations are performed by using the perturbation theory in the coupling between the dots, while the local density of states of a quantum dot attached to a given external lead is determined with the aid of the numerical renormalization group method. We demonstrate that the examined device can exhibit considerable positive or inverse tunnel magnetoresistance. It can be also a source of highly spin-polarized current. Importantly, the spin-resolved transport properties can be controlled by gate and bias voltages and depend on the angle between the magnetizations of the ferromagnets.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the magnetoresistive properties of a spin valve based on a double quantum dot attached to ferromagnetic leads with noncollinear alignment of magnetic moments. It is assumed that each dot is strongly coupled to its own ferromagnetic electrode, while the hopping between the dots is relatively weak. The calculations are performed by using the perturbation theory in the coupling between the dots, while the local density of states of a quantum dot attached to a given external lead is determined with the aid of the numerical renormalization group method. We demonstrate that the examined device can exhibit considerable positive or inverse tunnel magnetoresistance. It can be also a source of highly spin-polarized current. Importantly, the spin-resolved transport properties can be controlled by gate and bias voltages and depend on the angle between the magnetizations of the ferromagnets. |
| 19. | Piotr Trocha, Emil Siuda, Ireneusz Weymann Spin-polarized transport in quadruple quantum dots attached to ferromagnetic leads Journal of Magnetism and Magnetic Materials, 546 (168835), 2022. @article{Trocha2022b, title = {Spin-polarized transport in quadruple quantum dots attached to ferromagnetic leads}, author = {Piotr Trocha and Emil Siuda and Ireneusz Weymann}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321010453}, doi = {10.1016/j.jmmm.2021.168835}, year = {2022}, date = {2022-03-15}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {546}, number = {168835}, abstract = {Motivated by the experimental evidence of the Nagaoka ferromagnetism in quantum dot systems by Dehollain et al. (2020), we search for possible confirmation of such kind of ferromagnetism by analyzing the spin-resolved transport properties of a quadruple quantum dot system focusing on the linear response regime. In particular, we consider four quantum dots arranged in a two-by-two square lattice, coupled to external ferromagnetic source and drain electrodes. Turning on and off the specific conditions for the Nagaoka ferromagnetism to occur by changing the value of the intra-dot Coulomb interactions, we determine the transport coefficients, including the linear conductance, tunnel magnetoresistance and current spin polarization. We show that a sign change of the current spin polarization may be an indication of a ferromagnetic order of Nagaoka type which develops in the system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Motivated by the experimental evidence of the Nagaoka ferromagnetism in quantum dot systems by Dehollain et al. (2020), we search for possible confirmation of such kind of ferromagnetism by analyzing the spin-resolved transport properties of a quadruple quantum dot system focusing on the linear response regime. In particular, we consider four quantum dots arranged in a two-by-two square lattice, coupled to external ferromagnetic source and drain electrodes. Turning on and off the specific conditions for the Nagaoka ferromagnetism to occur by changing the value of the intra-dot Coulomb interactions, we determine the transport coefficients, including the linear conductance, tunnel magnetoresistance and current spin polarization. We show that a sign change of the current spin polarization may be an indication of a ferromagnetic order of Nagaoka type which develops in the system. |
| 18. | Piotr Busz, Damian Tomaszewski, Jan Martinek Exchange field determination in a quantum dot spin valve by the spin dynamics Journal of Magnetism and Magnetic Materials, 546 , pp. 168831, 2022. @article{Busz2022, title = {Exchange field determination in a quantum dot spin valve by the spin dynamics}, author = {Piotr Busz and Damian Tomaszewski and Jan Martinek}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321010428}, doi = {10.1016/j.jmmm.2021.168831}, year = {2022}, date = {2022-03-15}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {546}, pages = {168831}, abstract = {We develop the theory of the electron transport through quantum dot weakly coupled to ferromagnetic leads with noncollinear magnetization directions, that has been studied in recent experiments. One can observe much richer transport behavior of the canted quantum dot spin valves, as compared to single magnetic tunnel junctions, that relies on the possibility to generate a nonequilibrium accumulated spin on the quantum dot and the presence of the exchange interaction between dot and electrodes, depending on system parameters such as gate and bias voltages, the charging energy, an asymmetry of the tunnel couplings, and the external magnetic field. We demonstrate that one can extract information about spin dynamics on quantum dot from the dc current–voltage characteristic even at the linear response, and detect the exchange field similarly to the FMR (ferromagnetic resonance) experiment. This exchange field can be widely used in nano-spinelectronics, as a local field controlled by the gate or bias voltages also at high temperatures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We develop the theory of the electron transport through quantum dot weakly coupled to ferromagnetic leads with noncollinear magnetization directions, that has been studied in recent experiments. One can observe much richer transport behavior of the canted quantum dot spin valves, as compared to single magnetic tunnel junctions, that relies on the possibility to generate a nonequilibrium accumulated spin on the quantum dot and the presence of the exchange interaction between dot and electrodes, depending on system parameters such as gate and bias voltages, the charging energy, an asymmetry of the tunnel couplings, and the external magnetic field. We demonstrate that one can extract information about spin dynamics on quantum dot from the dc current–voltage characteristic even at the linear response, and detect the exchange field similarly to the FMR (ferromagnetic resonance) experiment. This exchange field can be widely used in nano-spinelectronics, as a local field controlled by the gate or bias voltages also at high temperatures. |
| 17. | Wojciech Rudziński Effect of single-ion anisotropy on magnons in the VSe2 bilayer antiferromagnet J. Magn. Magn. Mater., 546 , pp. 168687, 2022, ISSN: 0304-8853. @article{Rudziński2022, title = {Effect of single-ion anisotropy on magnons in the VSe2 bilayer antiferromagnet}, author = {Wojciech Rudziński}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321009239?via%3Dihub}, doi = {10.1016/j.jmmm.2021.168687}, issn = {0304-8853}, year = {2022}, date = {2022-03-15}, journal = {J. Magn. Magn. Mater.}, volume = {546}, pages = {168687}, abstract = {Spectrum of spin waves (magnons) in the two-dimensional bilayer antiferromagnet based on the VSe 2 is studied theoretically. The vanadium atoms within individual layers are coupled ferromagnetically, while the exchange coupling between V atoms located in different planes is antiferromagnetic. The magnon dispersion relation and its dependence on magnetic anisotropy is analyzed in the regime of weak external magnetic field. The spin-wave spectra are derived within the spin-wave theory of antiferromagnets in terms of the Holstein–Primakoff transformation combined with the Bogolubov diagonalization scheme. The magnon dispersion features are discussed in case of the T-type stacking of the VSe2 bilayer.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Spectrum of spin waves (magnons) in the two-dimensional bilayer antiferromagnet based on the VSe 2 is studied theoretically. The vanadium atoms within individual layers are coupled ferromagnetically, while the exchange coupling between V atoms located in different planes is antiferromagnetic. The magnon dispersion relation and its dependence on magnetic anisotropy is analyzed in the regime of weak external magnetic field. The spin-wave spectra are derived within the spin-wave theory of antiferromagnets in terms of the Holstein–Primakoff transformation combined with the Bogolubov diagonalization scheme. The magnon dispersion features are discussed in case of the T-type stacking of the VSe2 bilayer. |
| 16. | Kateryna Boboshko, Anna Dyrdał, Józef Barnaś Journal of Magnetism and Magnetic Materials, 545 , pp. 168698, 2022. @article{Boboshko2022, title = {Bilinear magnetoresistance in topological insulators: The role of spin–orbit scattering on impurities}, author = {Kateryna Boboshko and Anna Dyrdał and Józef Barnaś}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321009318}, doi = {10.1016/j.jmmm.2021.168698}, year = {2022}, date = {2022-03-01}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {545}, pages = {168698}, abstract = {Bilinear magnetoresistance (BMR) is a new kind of magnetoresistance, that scales linearly with electric and magnetic fields. This magnetoresistance occurs in systems with strong spin–orbit interaction. Additionally, this interaction also leads to quadratic magnetoresistance (QMR). We consider theoretically BMR and QMR in surface states of 3D topological insulators, and propose a new mechanism that leads to these effects. This mechanism is based on scattering on spin–orbit impurities. Accordingly, we assume the minimal model of surface electronic states in a single independent surface of a TI, and calculate both BMR and QMR induced as an interplay of current-induced spin polarization (or equivalently effective spin–orbit field) and spin–orbit scattering on impurities. We present detailed characteristics of both BMR and QMR, and compare our results with those obtained for TIs with spin-momentum locking inhomogeneities and hexagonal warping of the Dirac cones.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Bilinear magnetoresistance (BMR) is a new kind of magnetoresistance, that scales linearly with electric and magnetic fields. This magnetoresistance occurs in systems with strong spin–orbit interaction. Additionally, this interaction also leads to quadratic magnetoresistance (QMR). We consider theoretically BMR and QMR in surface states of 3D topological insulators, and propose a new mechanism that leads to these effects. This mechanism is based on scattering on spin–orbit impurities. Accordingly, we assume the minimal model of surface electronic states in a single independent surface of a TI, and calculate both BMR and QMR induced as an interplay of current-induced spin polarization (or equivalently effective spin–orbit field) and spin–orbit scattering on impurities. We present detailed characteristics of both BMR and QMR, and compare our results with those obtained for TIs with spin-momentum locking inhomogeneities and hexagonal warping of the Dirac cones. |
| 15. | Kacper Wrześniewski Journal of Magnetism and Magnetic Materials, 545 , pp. 168703, 2022. @article{Wrześniewski2022b, title = {Interplay of dark states and superconducting correlations in charge transport through quantum dot trimers}, author = {Kacper Wrześniewski}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321009331}, doi = {10.1016/j.jmmm.2021.168703}, year = {2022}, date = {2022-03-01}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {545}, pages = {168703}, abstract = {Electronic transport through a hybrid triple quantum dot system is theoretically studied by means of the real-time diagrammatic technique in the lowest order of perturbation theory. The central part of the system is arranged in a triangular geometry, with two quantum dots weakly coupled to metallic electrodes, while the third dot is proximitized by an s-wave superconductor. The focus is put on the transport regimes, where one- and two-electron dark states are formed due to the destructive interference of the electronic wavefunctions. This effect greatly influences the properties of the system, leading to the coherent population trapping and consequently to current blockade, negative differential conductance and enhanced shot-noise. It is shown that the presence of the superconducting pairing correlations in the system can lift the dark state blockade and reduce the shot-noise. Moreover, the current oscillations due to the magnetic flux enclosed by the triangular structure and the effect of superconducting correlations are considered. When the dark state has eigenenergy near the chemical potential of superconducting electrode, the amplitude of oscillations is strongly reduced while the current blockade is lifted. However, when the eigenenergy of the dark state is shifted away from the chemical potential of superconducting lead, the current oscillations remain unaffected.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electronic transport through a hybrid triple quantum dot system is theoretically studied by means of the real-time diagrammatic technique in the lowest order of perturbation theory. The central part of the system is arranged in a triangular geometry, with two quantum dots weakly coupled to metallic electrodes, while the third dot is proximitized by an s-wave superconductor. The focus is put on the transport regimes, where one- and two-electron dark states are formed due to the destructive interference of the electronic wavefunctions. This effect greatly influences the properties of the system, leading to the coherent population trapping and consequently to current blockade, negative differential conductance and enhanced shot-noise. It is shown that the presence of the superconducting pairing correlations in the system can lift the dark state blockade and reduce the shot-noise. Moreover, the current oscillations due to the magnetic flux enclosed by the triangular structure and the effect of superconducting correlations are considered. When the dark state has eigenenergy near the chemical potential of superconducting electrode, the amplitude of oscillations is strongly reduced while the current blockade is lifted. However, when the eigenenergy of the dark state is shifted away from the chemical potential of superconducting lead, the current oscillations remain unaffected. |
| 14. | Piotr Majek, Krzysztof P. Wójcik,, Ireneusz Weymann Spin-resolved thermal signatures of Majorana-Kondo interplay in double quantum dots Phys. Rev. B, 105 , pp. 075418, 2022. @article{Majek2022b, title = {Spin-resolved thermal signatures of Majorana-Kondo interplay in double quantum dots}, author = {Piotr Majek and Krzysztof P. Wójcik, and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.075418}, doi = {10.1103/PhysRevB.105.075418}, year = {2022}, date = {2022-02-17}, journal = {Phys. Rev. B}, volume = {105}, pages = {075418}, abstract = {We investigate theoretically the thermoelectric transport properties of a T-shaped double quantum dot side-coupled to a topological superconducting nanowire hosting Majorana zero-energy modes. The calculations are performed using the numerical renormalization group method focusing on the transport regime, where the system exhibits the two-stage Kondo effect. It is shown that the leakage of Majorana quasiparticles into the double dot system results in a half-suppression of the second stage of the Kondo effect, which is revealed through fractional values of the charge and heat conductances and gives rise to new resonances in the Seebeck coefficient. The heat conductance is found to satisfy a modified Wiedemann-Franz law. Finally, the interplay of Majorana-induced interference with strong electron correlations is discussed in the behavior of the spin Seebeck effect, which is a unique phenomenon of the considered setup.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We investigate theoretically the thermoelectric transport properties of a T-shaped double quantum dot side-coupled to a topological superconducting nanowire hosting Majorana zero-energy modes. The calculations are performed using the numerical renormalization group method focusing on the transport regime, where the system exhibits the two-stage Kondo effect. It is shown that the leakage of Majorana quasiparticles into the double dot system results in a half-suppression of the second stage of the Kondo effect, which is revealed through fractional values of the charge and heat conductances and gives rise to new resonances in the Seebeck coefficient. The heat conductance is found to satisfy a modified Wiedemann-Franz law. Finally, the interplay of Majorana-induced interference with strong electron correlations is discussed in the behavior of the spin Seebeck effect, which is a unique phenomenon of the considered setup. |
| 13. | V. A. Stephanovich, E. V. Kirichenko, V. K. Dugaev, Józef Barnaś Dynamic Friedel oscillations on the surface of a topological insulator Phys. Rev. B, 105 , pp. 075306, 2022. @article{Stephanovich2022, title = {Dynamic Friedel oscillations on the surface of a topological insulator}, author = {V. A. Stephanovich and E. V. Kirichenko and V. K. Dugaev and Józef Barnaś}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.075306}, doi = {10.1103/PhysRevB.105.075306}, year = {2022}, date = {2022-02-14}, journal = {Phys. Rev. B}, volume = {105}, pages = {075306}, abstract = {We study theoretically the dynamic Friedel oscillations of electrons at the surface of a topological insulator (TI) that are generated by the rotation of a localized impurity spin. We show that the spin-orbit interaction (SOI) in Rashba form, which is an integral part of the TI Hamiltonian, yields a highly anisotropic response to the localized spin rotation. As a result, the response to a flip of a localized spin z projection involves the reaction of all x, y, and z components of the local magnetization. Additionally, the dynamic spin moment (and thus also Friedel oscillations) emitted by the localized dynamical spin depends on the orientation in the TI plane. The resulting unusual dynamics is due to the interplay of SOI and Ruderman-Kittel-Kasuya-Yoshida interactions. This provides the basis for manipulation of the spin transport in topological insulators decorated with localized impurity spins, which may be important for technological applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study theoretically the dynamic Friedel oscillations of electrons at the surface of a topological insulator (TI) that are generated by the rotation of a localized impurity spin. We show that the spin-orbit interaction (SOI) in Rashba form, which is an integral part of the TI Hamiltonian, yields a highly anisotropic response to the localized spin rotation. As a result, the response to a flip of a localized spin z projection involves the reaction of all x, y, and z components of the local magnetization. Additionally, the dynamic spin moment (and thus also Friedel oscillations) emitted by the localized dynamical spin depends on the orientation in the TI plane. The resulting unusual dynamics is due to the interplay of SOI and Ruderman-Kittel-Kasuya-Yoshida interactions. This provides the basis for manipulation of the spin transport in topological insulators decorated with localized impurity spins, which may be important for technological applications. |
| 12. | Damian Tomaszewski, Piotr Busz, Jan Martinek Kondo effect in the presence of the spin accumulation and non-equilibrium spin currents Journal of Magnetism and Magnetic Materials, 542 , pp. 168592, 2022. @article{Tomaszewski2022, title = {Kondo effect in the presence of the spin accumulation and non-equilibrium spin currents}, author = {Damian Tomaszewski and Piotr Busz and Jan Martinek}, url = {https://www.sciencedirect.com/science/article/pii/S0304885321008362}, doi = {10.1016/j.jmmm.2021.168592}, year = {2022}, date = {2022-01-15}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {542}, pages = {168592}, abstract = {We present a theoretical description of the spin accumulation effect in metallic Fermi leads on the Kondo effect in the quantum dot attached to those. It has been shown that the spin accumulation by breaking the spin symmetry leads to the suppression of the Kondo effect in some cases. In order to better understand the observed effects, we analyze the spin currents in the system, depending on the spin accumulation of the electrodes, for both symmetrical and anti-symmetrical configuration of spin accumulation. We demonstrate that in the absence of the Kondo resonance splitting the suppression of the Kondo effect is related to the presence of the non-equilibrium spin current in the system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a theoretical description of the spin accumulation effect in metallic Fermi leads on the Kondo effect in the quantum dot attached to those. It has been shown that the spin accumulation by breaking the spin symmetry leads to the suppression of the Kondo effect in some cases. In order to better understand the observed effects, we analyze the spin currents in the system, depending on the spin accumulation of the electrodes, for both symmetrical and anti-symmetrical configuration of spin accumulation. We demonstrate that in the absence of the Kondo resonance splitting the suppression of the Kondo effect is related to the presence of the non-equilibrium spin current in the system. |
| 11. | Anna Krzyżewska, Anna Dyrdał Physica E, 135 , pp. 114961, 2022, ISSN: 1386-9477. @article{physicaE_2021.114961, title = {Non-equilibrium spin polarization in magnetic two-dimensional electron gas with k-linear and k-cubed Dresselhaus spin–orbit interaction}, author = {Anna Krzyżewska and Anna Dyrdał}, url = {https://doi.org/10.1016/j.physe.2021.114961}, doi = {10.1016/j.physe.2021.114961}, issn = {1386-9477}, year = {2022}, date = {2022-01-01}, journal = {Physica E}, volume = {135}, pages = {114961}, publisher = {North-Holland}, abstract = {The current-induced spin polarization (CISP) of charge carriers is one of the main mechanisms of spin-to-charge interconversion effects that can be used in new spintronics devices. Here, CISP is studied theoreticallyin symmetric quantum wells growing in [001] crystallographic direction, where both𝑘-linear and𝑘-cubedDresselhaus spin–orbit interactions are present. The exchange interaction responsible for perpendicular to planenet magnetization is also taken into account. The main focus is on the influence of cubic Dresselhaus termon CISP and the interplay between spin–orbit interaction (SOI) and the exchange field. The analytical andnumerical results are derived within the linear response theory and Matsubara Green’s function formalism.Apart from detailed numerical results, we also provide some analytical expressions that may be usefulfor interpretation of experimental results and for characterization of quantum wells with Dresselhaus SOI.Analytical expressions for the relevant Berry curvature are also derived, and it is shown that the Berrycurvature in magnetic 2DEG with cubic Dresselhaus interaction oscillates in the𝑘-space, while its averagedvalue is reduced. We also analyze the temperature behavior of CISP and calculate the low-temperature spinpolarizability due to heat current.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The current-induced spin polarization (CISP) of charge carriers is one of the main mechanisms of spin-to-charge interconversion effects that can be used in new spintronics devices. Here, CISP is studied theoreticallyin symmetric quantum wells growing in [001] crystallographic direction, where both𝑘-linear and𝑘-cubedDresselhaus spin–orbit interactions are present. The exchange interaction responsible for perpendicular to planenet magnetization is also taken into account. The main focus is on the influence of cubic Dresselhaus termon CISP and the interplay between spin–orbit interaction (SOI) and the exchange field. The analytical andnumerical results are derived within the linear response theory and Matsubara Green’s function formalism.Apart from detailed numerical results, we also provide some analytical expressions that may be usefulfor interpretation of experimental results and for characterization of quantum wells with Dresselhaus SOI.Analytical expressions for the relevant Berry curvature are also derived, and it is shown that the Berrycurvature in magnetic 2DEG with cubic Dresselhaus interaction oscillates in the𝑘-space, while its averagedvalue is reduced. We also analyze the temperature behavior of CISP and calculate the low-temperature spinpolarizability due to heat current. |
2021 |
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| 10. | Michał Inglot, Vitalii K. Dugaev, Anna Dyrdał, Józef Barnaś Phys. Rev. B, 104 (21), pp. 214408, 2021, ISSN: 2469-9969. @article{Inglot2021, title = {Graphene with Rashba spin-orbit interaction and coupling to a magnetic layer: Electron states localized at the domain wall}, author = {Michał Inglot and Vitalii K. Dugaev and Anna Dyrdał and Józef Barnaś}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.214408}, doi = {10.1103/PhysRevB.104.214408}, issn = {2469-9969}, year = {2021}, date = {2021-12-06}, journal = {Phys. Rev. B}, volume = {104}, number = {21}, pages = {214408}, abstract = {Electron states localized at a magnetic domain wall in a graphene with Rashba spin-orbit interaction and coupled to a magnetic layer are studied theoretically. It is shown that two one-dimensional bands of edge modes propagating along the domain wall emerge in the energy gap for each Dirac point, and the modes associated with different Dirac points K and K′ are the same. The coefficients describing decay of the corresponding wave functions with distance from the domain wall contain generally real and imaginary terms. Numerical results on the local spin density and on the total spin expected in the edge states characterized by the wave number ky are presented and discussed. The Chern number for a single magnetic domain on graphene indicates that the system is in the quantum anomalous Hall phase, with two chiral modes at the edges. In turn, the number of modes localized at the domain wall is determined by the difference in Chern numbers on both sides of the wall. These numbers are equal to 2 and −2, respectively, so there are four modes localized at the domain wall.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electron states localized at a magnetic domain wall in a graphene with Rashba spin-orbit interaction and coupled to a magnetic layer are studied theoretically. It is shown that two one-dimensional bands of edge modes propagating along the domain wall emerge in the energy gap for each Dirac point, and the modes associated with different Dirac points K and K′ are the same. The coefficients describing decay of the corresponding wave functions with distance from the domain wall contain generally real and imaginary terms. Numerical results on the local spin density and on the total spin expected in the edge states characterized by the wave number ky are presented and discussed. The Chern number for a single magnetic domain on graphene indicates that the system is in the quantum anomalous Hall phase, with two chiral modes at the edges. In turn, the number of modes localized at the domain wall is determined by the difference in Chern numbers on both sides of the wall. These numbers are equal to 2 and −2, respectively, so there are four modes localized at the domain wall. |
| 9. | Cătălin Paşcu Moca, Ireneusz Weymann, Miklós Antal Werner, Gergely Zaránd Kondo Cloud in a Superconductor Phys. Rev. Lett., 127 , pp. 186804, 2021. @article{Moca2021, title = {Kondo Cloud in a Superconductor}, author = {Cătălin Paşcu Moca and Ireneusz Weymann and Miklós Antal Werner and Gergely Zaránd}, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.186804}, doi = {10.1103/PhysRevLett.127.186804}, year = {2021}, date = {2021-10-27}, journal = {Phys. Rev. Lett.}, volume = {127}, pages = {186804}, abstract = {Magnetic impurities embedded in a metal are screened by the Kondo effect, signaled by the formation of an extended correlation cloud, the so-called Kondo or screening cloud. In a superconductor, the Kondo state turns into subgap Yu-Shiba-Rusinov states, and a quantum phase transition occurs between screened and unscreened phases once the superconducting energy gap Δ exceeds sufficiently the Kondo temperature, TK. Here we show that, although the Kondo state does not form in the unscreened phase, the Kondo cloud does exist in both quantum phases. However, while screening is complete in the screened phase, it is only partial in the unscreened phase. Compensation, a quantity introduced to characterize the integrity of the cloud, is universal, and shown to be related to the magnetic impurities’ g factor, monitored experimentally by bias spectroscopy.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Magnetic impurities embedded in a metal are screened by the Kondo effect, signaled by the formation of an extended correlation cloud, the so-called Kondo or screening cloud. In a superconductor, the Kondo state turns into subgap Yu-Shiba-Rusinov states, and a quantum phase transition occurs between screened and unscreened phases once the superconducting energy gap Δ exceeds sufficiently the Kondo temperature, TK. Here we show that, although the Kondo state does not form in the unscreened phase, the Kondo cloud does exist in both quantum phases. However, while screening is complete in the screened phase, it is only partial in the unscreened phase. Compensation, a quantity introduced to characterize the integrity of the cloud, is universal, and shown to be related to the magnetic impurities’ g factor, monitored experimentally by bias spectroscopy. |
| 8. | Damian Tomaszewski, Piotr Busz, Jan Martinek Spin-current Kondo effect: Kondo effect in the presence of spin accumulation Phys. Rev. B, 104 , pp. 125108, 2021. @article{Tomaszewski2021, title = {Spin-current Kondo effect: Kondo effect in the presence of spin accumulation}, author = {Damian Tomaszewski and Piotr Busz and Jan Martinek}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.125108}, doi = {10.1103/PhysRevB.104.125108}, year = {2021}, date = {2021-09-07}, journal = {Phys. Rev. B}, volume = {104}, pages = {125108}, abstract = {We present a detailed theoretical description of the influence of the spin accumulation in metallic Fermi leads on the Kondo effect in systems such as quantum dots and Kondo alloys. We discuss an interplay of the spin accumulation, magnetic field, and ferromagnetic leads spin polarization on the Kondo spin-dependent densities of states, conductance, and resistance. It has been shown that the presence of the above-mentioned factors by breaking the spin symmetry leads to the suppression of the Kondo effect. However, for appropriately selected parameter values, these effects can compensate each other, which may lead to the restoration of the Kondo effect in the analyzed systems. We also address some recent experiments related to the spin current in the Kondo alloys.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a detailed theoretical description of the influence of the spin accumulation in metallic Fermi leads on the Kondo effect in systems such as quantum dots and Kondo alloys. We discuss an interplay of the spin accumulation, magnetic field, and ferromagnetic leads spin polarization on the Kondo spin-dependent densities of states, conductance, and resistance. It has been shown that the presence of the above-mentioned factors by breaking the spin symmetry leads to the suppression of the Kondo effect. However, for appropriately selected parameter values, these effects can compensate each other, which may lead to the restoration of the Kondo effect in the analyzed systems. We also address some recent experiments related to the spin current in the Kondo alloys. |
| 7. | Piotr Majek, Ireneusz Weymann Majorana mode leaking into a spin-charge entangled double quantum dot Phys. Rev. B, 104 , pp. 085416, 2021. @article{Majek2021, title = {Majorana mode leaking into a spin-charge entangled double quantum dot}, author = {Piotr Majek and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.085416}, doi = {10.1103/PhysRevB.104.085416}, year = {2021}, date = {2021-08-12}, journal = {Phys. Rev. B}, volume = {104}, pages = {085416}, abstract = {The signatures of Majorana zero-energy mode leaking into a spin-charge entangled double quantum dot are investigated theoretically in the strong electron correlation regime. The considered setup consists of two capacitively coupled quantum dots attached to external contacts and side-attached to topological superconducting wire hosting Majorana quasiparticles. We show that the presence of Majorana mode gives rise to unique features in the local density of states in the SU(4) Kondo regime. Moreover, it greatly modifies the gate voltage dependence of the linear conductance, leading to fractional values of the conductance. We also analyze the effect of a finite length of topological wire and demonstrate that nonzero overlap of Majorana modes at the ends of the wire is revealed in local extrema present in the local density of states of the dot coupled directly to the wire. The calculations are performed with the aid of the numerical renormalization group method.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The signatures of Majorana zero-energy mode leaking into a spin-charge entangled double quantum dot are investigated theoretically in the strong electron correlation regime. The considered setup consists of two capacitively coupled quantum dots attached to external contacts and side-attached to topological superconducting wire hosting Majorana quasiparticles. We show that the presence of Majorana mode gives rise to unique features in the local density of states in the SU(4) Kondo regime. Moreover, it greatly modifies the gate voltage dependence of the linear conductance, leading to fractional values of the conductance. We also analyze the effect of a finite length of topological wire and demonstrate that nonzero overlap of Majorana modes at the ends of the wire is revealed in local extrema present in the local density of states of the dot coupled directly to the wire. The calculations are performed with the aid of the numerical renormalization group method. |
| 6. | Patrycja Tulewicz, Kacper Wrześniewski, Szabolcs Csonka, Ireneusz Weymann Large Voltage-Tunable Spin Valve Based on a Double Quantum Dot Phys. Rev. Applied, 16 , pp. 014029, 2021. @article{Tulewicz2021, title = {Large Voltage-Tunable Spin Valve Based on a Double Quantum Dot}, author = {Patrycja Tulewicz and Kacper Wrześniewski and Szabolcs Csonka and Ireneusz Weymann}, url = {https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.16.014029}, doi = {https://doi.org/10.1103/PhysRevApplied.16.014029}, year = {2021}, date = {2021-07-12}, journal = {Phys. Rev. Applied}, volume = {16}, pages = {014029}, abstract = {We study the spin-dependent transport properties of a spin valve based on a double quantum dot. Each quantum dot is assumed to be strongly coupled to its own ferromagnetic lead, while the coupling between the dots is relatively weak. The current flowing through the system is determined within perturbation theory in the hopping between the dots, whereas the spectrum of a quantum-dot–ferromagnetic-lead subsystem is determined by means of the numerical renormalization group method. The spin-dependent charge fluctuations between ferromagnets and quantum dots generate an effective exchange field, which splits the double-dot levels. Such a field can be controlled, separately for each quantum dot, by the gate voltages or by changing the magnetic configuration of the external leads. We demonstrate that the considered double-quantum-dot spin-valve setup exhibits enhanced magnetoresistive properties, including both normal and inverse tunnel magnetoresistance. We also show that this system allows for the generation of highly spin-polarized currents, which can be controlled by purely electrical means. The considered double quantum dot with ferromagnetic contacts can thus serve as an efficient voltage-tunable spin valve characterized by high output parameters.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the spin-dependent transport properties of a spin valve based on a double quantum dot. Each quantum dot is assumed to be strongly coupled to its own ferromagnetic lead, while the coupling between the dots is relatively weak. The current flowing through the system is determined within perturbation theory in the hopping between the dots, whereas the spectrum of a quantum-dot–ferromagnetic-lead subsystem is determined by means of the numerical renormalization group method. The spin-dependent charge fluctuations between ferromagnets and quantum dots generate an effective exchange field, which splits the double-dot levels. Such a field can be controlled, separately for each quantum dot, by the gate voltages or by changing the magnetic configuration of the external leads. We demonstrate that the considered double-quantum-dot spin-valve setup exhibits enhanced magnetoresistive properties, including both normal and inverse tunnel magnetoresistance. We also show that this system allows for the generation of highly spin-polarized currents, which can be controlled by purely electrical means. The considered double quantum dot with ferromagnetic contacts can thus serve as an efficient voltage-tunable spin valve characterized by high output parameters. |
| 5. | Ryszard Taranko, Kacper Wrześniewski, Bartłomiej Baran, Ireneusz Weymann, Tadeusz Domański Phys. Rev. B, 103 , pp. 165430, 2021. @article{Taranko2021, title = {Transient effects in a double quantum dot sandwiched laterally between superconducting and metallic leads}, author = {Ryszard Taranko and Kacper Wrześniewski and Bartłomiej Baran and Ireneusz Weymann and Tadeusz Domański}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.165430}, doi = {10.1103/PhysRevB.103.165430}, year = {2021}, date = {2021-04-29}, journal = {Phys. Rev. B}, volume = {103}, pages = {165430}, abstract = {We study the transient phenomena appearing in a subgap region of the double quantum dot coupled in series between the superconducting and normal metallic leads, focusing on the development of the superconducting proximity effect. For the uncorrelated nanostructure we derive explicit expressions of the time-dependent occupancies in both quantum dots, charge currents, and electron pairing induced on individual dots and between them. We show that the initial configurations substantially affect the dynamical processes, in which the in-gap bound states emerge upon coupling the double quantum dot to the superconducting reservoir. In particular, the superconducting proximity effect would be temporarily blocked whenever the quantum dots are initially singly occupied. Such triplet/Andreev blockade has been recently reported experimentally for double quantum dots embedded in the Josephson [Bouman et al., Phys. Rev. B 102, 220505 (2020)] and Andreev [Zhang et al., arXiv:2102.03283 (2021)] junctions. We also address the role of correlation effects within the lowest-order decoupling scheme and by the time-dependent numerical renormalization group calculations. Competition of the repulsive Coulomb interactions with the superconducting proximity effect leads to renormalization of the in-gap quasiparticles, speeding up the quantum oscillations and narrowing a region of transient phenomena, whereas the dynamical Andreev blockade is well pronounced in the weak interdot coupling limit. We propose feasible methods for detecting the characteristic timescales that could be observable by the Andreev spectroscopy.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the transient phenomena appearing in a subgap region of the double quantum dot coupled in series between the superconducting and normal metallic leads, focusing on the development of the superconducting proximity effect. For the uncorrelated nanostructure we derive explicit expressions of the time-dependent occupancies in both quantum dots, charge currents, and electron pairing induced on individual dots and between them. We show that the initial configurations substantially affect the dynamical processes, in which the in-gap bound states emerge upon coupling the double quantum dot to the superconducting reservoir. In particular, the superconducting proximity effect would be temporarily blocked whenever the quantum dots are initially singly occupied. Such triplet/Andreev blockade has been recently reported experimentally for double quantum dots embedded in the Josephson [Bouman et al., Phys. Rev. B 102, 220505 (2020)] and Andreev [Zhang et al., arXiv:2102.03283 (2021)] junctions. We also address the role of correlation effects within the lowest-order decoupling scheme and by the time-dependent numerical renormalization group calculations. Competition of the repulsive Coulomb interactions with the superconducting proximity effect leads to renormalization of the in-gap quasiparticles, speeding up the quantum oscillations and narrowing a region of transient phenomena, whereas the dynamical Andreev blockade is well pronounced in the weak interdot coupling limit. We propose feasible methods for detecting the characteristic timescales that could be observable by the Andreev spectroscopy. |
| 4. | Anand Manaparambil, Ireneusz Weymann Spin Seebeck effect of correlated magnetic molecules Sci. Rep., 11 (9192), pp. 1-15, 2021. @article{Man2021April, title = {Spin Seebeck effect of correlated magnetic molecules}, author = {Anand Manaparambil and Ireneusz Weymann}, url = {https://www.nature.com/articles/s41598-021-88373-7}, doi = {10.1038/s41598-021-88373-7}, year = {2021}, date = {2021-04-28}, journal = {Sci. Rep.}, volume = {11}, number = {9192}, pages = {1-15}, abstract = {In this paper we investigate the spin-resolved thermoelectric properties of strongly correlated molecular junctions in the linear response regime. The magnetic molecule is modeled by a single orbital level to which the molecular core spin is attached by an exchange interaction. Using the numerical renormalization group method we analyze the behavior of the (spin) Seebeck effect, heat conductance and figure of merit for different model parameters of the molecule. We show that the thermopower strongly depends on the strength and type of the exchange interaction as well as the molecule’s magnetic anisotropy. When the molecule is coupled to ferromagnetic leads, the thermoelectric properties reveal an interplay between the spin-resolved tunneling processes and intrinsic magnetic properties of the molecule. Moreover, in the case of finite spin accumulation in the leads, the system exhibits the spin Seebeck effect. We demonstrate that a considerable spin Seebeck effect can develop when the molecule exhibits an easy-plane magnetic anisotropy, while the sign of the spin thermopower depends on the type and magnitude of the molecule’s exchange interaction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper we investigate the spin-resolved thermoelectric properties of strongly correlated molecular junctions in the linear response regime. The magnetic molecule is modeled by a single orbital level to which the molecular core spin is attached by an exchange interaction. Using the numerical renormalization group method we analyze the behavior of the (spin) Seebeck effect, heat conductance and figure of merit for different model parameters of the molecule. We show that the thermopower strongly depends on the strength and type of the exchange interaction as well as the molecule’s magnetic anisotropy. When the molecule is coupled to ferromagnetic leads, the thermoelectric properties reveal an interplay between the spin-resolved tunneling processes and intrinsic magnetic properties of the molecule. Moreover, in the case of finite spin accumulation in the leads, the system exhibits the spin Seebeck effect. We demonstrate that a considerable spin Seebeck effect can develop when the molecule exhibits an easy-plane magnetic anisotropy, while the sign of the spin thermopower depends on the type and magnitude of the molecule’s exchange interaction. |
| 3. | Kacper Wrześniewski, Bartłomiej Baran, Ryszard Taranko, Tadeusz Domański, Ireneusz Weymann Phys. Rev. B, 103 , pp. 155420, 2021. @article{Wrzesniewski2021April, title = {Quench dynamics of a correlated quantum dot sandwiched between normal-metal and superconducting leads}, author = {Kacper Wrześniewski and Bartłomiej Baran and Ryszard Taranko and Tadeusz Domański and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.155420}, doi = {https://doi.org/10.1103/PhysRevB.103.155420}, year = {2021}, date = {2021-04-22}, journal = {Phys. Rev. B}, volume = {103}, pages = {155420}, abstract = {Quantum system abruptly driven from its stationary phase can reveal nontrivial dynamics upon approaching a new final state. We investigate here such dynamics for a correlated quantum dot sandwiched between the metallic and superconducting leads, considering two types of quenches feasible experimentally. The first one is related to a sudden change of the coupling between the dot and the superconducting lead, while the other one is associated with an abrupt shift of the quantum dot energy level. Using the time-dependent numerical renormalization group method, we examine and quantify the interplay between the proximity induced electron pairing with correlations caused by the on-dot Coulomb repulsion. We determine and discuss the time-dependent charge occupancy, on-dot pair correlation, transient currents, and analyze the evolution of the subgap quasiparticles, which could be empirically observed in the tunneling conductance. To get some insight into the dynamics of a biased junction, we make use of a mean-field approximation. We reveal the signatures of the time-dependent 0-π transition and demonstrate that the evolution of local observables exhibits damped quantum oscillations with frequencies given by the energies of Andreev bound states}, keywords = {}, pubstate = {published}, tppubtype = {article} } Quantum system abruptly driven from its stationary phase can reveal nontrivial dynamics upon approaching a new final state. We investigate here such dynamics for a correlated quantum dot sandwiched between the metallic and superconducting leads, considering two types of quenches feasible experimentally. The first one is related to a sudden change of the coupling between the dot and the superconducting lead, while the other one is associated with an abrupt shift of the quantum dot energy level. Using the time-dependent numerical renormalization group method, we examine and quantify the interplay between the proximity induced electron pairing with correlations caused by the on-dot Coulomb repulsion. We determine and discuss the time-dependent charge occupancy, on-dot pair correlation, transient currents, and analyze the evolution of the subgap quasiparticles, which could be empirically observed in the tunneling conductance. To get some insight into the dynamics of a biased junction, we make use of a mean-field approximation. We reveal the signatures of the time-dependent 0-π transition and demonstrate that the evolution of local observables exhibits damped quantum oscillations with frequencies given by the energies of Andreev bound states |
| 2. | Kacper Wrześniewski, Ireneusz Weymann Magnetization dynamics in a Majorana-wire–quantum-dot setup Phys. Rev. B, 103 , pp. 125413, 2021. @article{Wrzesniewski2021Mar, title = {Magnetization dynamics in a Majorana-wire–quantum-dot setup}, author = {Kacper Wrześniewski and Ireneusz Weymann}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.125413}, doi = {https://doi.org/10.1103/PhysRevB.103.125413}, year = {2021}, date = {2021-03-11}, journal = {Phys. Rev. B}, volume = {103}, pages = {125413}, abstract = {We theoretically study the quench dynamics of the local magnetization in a hybrid Majorana-wire–quantum-dot system coupled to external leads. In order to thoroughly understand the origin of the dot magnetization dynamics, we consider either normal metal or ferromagnetic electrodes. In the first case, the magnetization arises exclusively from the proximity to the topological superconductor hosting Majorana zero-energy modes and the associated development of an induced exchange field. We predict a nonmonotonic dependence of the dot's magnetization in the odd-occupation regime and show that the dynamics is governed by the magnitude of the coupling to Majorana wire. However, when the system is coupled to ferromagnetic leads, the ferromagnet and Majorana contributions to the effective exchange field are competing with each other and reveal a nontrivial dynamical behavior. As a result, the time-dependent magnetization can undergo multiple sign changes preceding the relaxation to a new thermal value. We also identify the transport regime, where fine tuning of the coupling to Majorana wire within a narrow range allows one to manipulate the magnetic state of the system. The effect of spin polarization of the leads and influence of the finite overlap between the Majorana edge modes are also examined. Moreover, we analyze the quench in the energy of the quantum dot orbital level and demonstrate that the rather straightforward charge dynamics can disguise nontrivial time evolution of the magnetization. Finally, we compare predicted dynamics with results obtained for quantum dot coupled to spin-polarized fermionic bound state instead of Majorana zero-energy mode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We theoretically study the quench dynamics of the local magnetization in a hybrid Majorana-wire–quantum-dot system coupled to external leads. In order to thoroughly understand the origin of the dot magnetization dynamics, we consider either normal metal or ferromagnetic electrodes. In the first case, the magnetization arises exclusively from the proximity to the topological superconductor hosting Majorana zero-energy modes and the associated development of an induced exchange field. We predict a nonmonotonic dependence of the dot's magnetization in the odd-occupation regime and show that the dynamics is governed by the magnitude of the coupling to Majorana wire. However, when the system is coupled to ferromagnetic leads, the ferromagnet and Majorana contributions to the effective exchange field are competing with each other and reveal a nontrivial dynamical behavior. As a result, the time-dependent magnetization can undergo multiple sign changes preceding the relaxation to a new thermal value. We also identify the transport regime, where fine tuning of the coupling to Majorana wire within a narrow range allows one to manipulate the magnetic state of the system. The effect of spin polarization of the leads and influence of the finite overlap between the Majorana edge modes are also examined. Moreover, we analyze the quench in the energy of the quantum dot orbital level and demonstrate that the rather straightforward charge dynamics can disguise nontrivial time evolution of the magnetization. Finally, we compare predicted dynamics with results obtained for quantum dot coupled to spin-polarized fermionic bound state instead of Majorana zero-energy mode. |
| 1. | Ricarda Pütt, Piotr Kozłowski, Irina Werner, Jan Griebel, Sebastian Schmitz, Jonas Warneke, Kirill Yu. Monakhov P2V3W15-Polyoxometalates Functionalized with Phthalocyaninato Y and Yb Moieties Inorg. Chem. , 60 (1), pp. 80-86, 2021, (PMID: 33180468). @article{Putt, title = {P2V3W15-Polyoxometalates Functionalized with Phthalocyaninato Y and Yb Moieties}, author = {Ricarda Pütt and Piotr Kozłowski and Irina Werner and Jan Griebel and Sebastian Schmitz and Jonas Warneke and Kirill Yu. Monakhov}, url = {https://doi.org/10.1021/acs.inorgchem.0c02257}, doi = {10.1021/acs.inorgchem.0c02257}, year = {2021}, date = {2021-01-01}, journal = {Inorg. Chem. }, volume = {60}, number = {1}, pages = {80-86}, abstract = {A tris(alkoxo)pyridine-augmented Wells–Dawson polyoxometalate (nBu4N)6[WD-Py] (WD = P2V3W15O59(OCH2)3C, Py = C5H4N) was functionalized with phthalocyaninato metal moieties (MPc where M = Y or Yb and Pc = C32H16N8) to afford (nBu4N)4[HWD-Py(MPc)] compounds. High-resolution mass spectrometry was used to detect and identify the hybrid assembly. The magnetism studies reveal substantial differences between M = Yb (monomeric, single-ion paramagnetism) and M = Y (containing dimers, radical character). The results of electronic paramagnetic resonance spectroscopy, SQUID magnetometry, and magnetochemical calculations indicate the presence of intramolecular charge transfer from the MPc moiety to the polyoxometalate and of intermolecular charge transfer from the MPc moiety of one molecule to the polyoxometalate unit of another molecule. These compounds with identified VIV ions represent unique examples of transition-metal/lanthanide complex-POM hybrid compounds with nonphotoinduced charge transfer between electron donor and acceptor centers.}, note = {PMID: 33180468}, keywords = {}, pubstate = {published}, tppubtype = {article} } A tris(alkoxo)pyridine-augmented Wells–Dawson polyoxometalate (nBu4N)6[WD-Py] (WD = P2V3W15O59(OCH2)3C, Py = C5H4N) was functionalized with phthalocyaninato metal moieties (MPc where M = Y or Yb and Pc = C32H16N8) to afford (nBu4N)4[HWD-Py(MPc)] compounds. High-resolution mass spectrometry was used to detect and identify the hybrid assembly. The magnetism studies reveal substantial differences between M = Yb (monomeric, single-ion paramagnetism) and M = Y (containing dimers, radical character). The results of electronic paramagnetic resonance spectroscopy, SQUID magnetometry, and magnetochemical calculations indicate the presence of intramolecular charge transfer from the MPc moiety to the polyoxometalate and of intermolecular charge transfer from the MPc moiety of one molecule to the polyoxometalate unit of another molecule. These compounds with identified VIV ions represent unique examples of transition-metal/lanthanide complex-POM hybrid compounds with nonphotoinduced charge transfer between electron donor and acceptor centers. |