@article{Zalom2024,
title = {Double quantum dot Andreev molecules: Phase diagrams and critical evaluation of effective models},
author = {Peter Zalom and Kacper Wrześniewski and Tomáš Novotný and Ireneusz Weymann},
url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.110.134506},
doi = {10.1103/PhysRevB.110.134506},
year = {2024},
date = {2024-10-07},
journal = {Physical Review B},
volume = {110},
pages = {134506},
abstract = {This paper systematically investigates the phase diagram of a parallel double-quantum-dot Andreev molecule, where the two quantum dots are coupled to a common superconducting lead. Using the numerical renormalization group method, we map out the evolution of the ground state across a wide parameter space of level detunings, size of the superconducting gap, lead couplings, and interdot coupling strength. The intricate phase diagrams feature singlet, doublet, and a relatively uncommon triplet ground states, with the latter being a distinct signature of strong lead-mediated interactions between the quantum dots. We benchmark the applicability of simplified effective models, including the atomic limit and zero-bandwidth approximations, in capturing the complex behavior of this parallel configuration. Our analysis reveals severe limitations of these models, underscoring the necessity for maximal caution when extrapolating beyond their tested validity. In particular, all effective models except for the extended version of the zero-bandwidth approximation failed in reproducing the triplet ground state and made several false predictions. These findings provide crucial insights for interpreting experimental observations and designing superconducting devices based on quantum-dot architectures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Taranko2024,
title = {Transient effects in quantum dots contacted via topological superconductor},
author = {Ryszard Taranko and Kacper Wrześniewski and Ireneusz Weymann and Tadeusz Domański},
url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.110.035413},
doi = {10.1103/PhysRevB.110.035413},
year = {2024},
date = {2024-07-10},
journal = {Physical Review B},
volume = {110},
pages = {035413},
abstract = {We investigate gradual development of the quasiparticle states in two quantum dots attached to opposite sides of the topological superconducting nanowire, hosting the boundary modes. Specifically, we explore the nonequilibrium cross-correlations transmitted between these quantum dots via the zero-energy Majorana modes. Our analytical and numerical results reveal the nonlocal features observable in the transient behavior of electron pairing, which subsequently cease while the hybrid structure evolves towards its asymptotic steady-state configuration. We estimate duration of these temporary phenomena. Using the nonperturbative scheme of the time-dependent numerical renormalization group technique we also analyze nonequilibrium signatures of the correlation effects competing with the proximity induced electron pairing. These dynamical processes could manifest themselves in braiding protocols imposed on the topological and/or conventional superconducting quantum bits, using superconducting hybrid nanostructures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Wrześniewski2024,
title = {Cross-correlations between currents and tunnel magnetoresistance in interacting double quantum dot-Majorana wire system},
author = {Kacper Wrześniewski and Ireneusz Weymann },
url = {https://link.springer.com/article/10.1038/s41598-024-58344-9},
doi = {10.1038/s41598-024-58344-9},
year = {2024},
date = {2024-04-03},
journal = {Scientific Reports},
volume = {14},
number = {7815},
abstract = {We theoretically investigate the spin and charge transport properties of a double quantum dot coupled to distinct edges of the nanowire hosting Majorana zero-energy modes. The focus is on the analysis of the currents flowing through the left and right junctions and their cross-correlations. We show that the system reveals very different transport properties depending on the detuning protocol of the quantum dot energy levels. For the symmetric detuning, the current dependencies reveal only two maxima associated with resonant tunneling, and currents in the left and right arms of the system reveal weak positive cross-correlations. On the other hand, for antisymmetric detuning, the flow of electrons into drains is maximized and strongly correlated in one bias voltage direction, while for the opposite bias direction a spin blockade is predicted. Furthermore, we observe a suppression of the current cross-correlations at a highly symmetric detuning point, indicating the involvement of the Majorana zero-energy modes in the transport processes. To gain insight into the role of the spin polarization of the Majorana edge states, we analyze the spin-dependent transport characteristics by considering the relationship between the spin canting angle, which describes the coupling of the Majorana modes to the spin of the quantum dots, and the magnetic configurations of the ferromagnetic drains. Moreover, we examine the non-local zero bias anomaly in the differential conductance, detailed analysis of which revealed a specific operational mode of the device that can facilitate the identification of the Majorana presence in the quantum dot-Majorana wire system. Finally, we also consider the transport properties in different magnetic configurations of the system and discuss the behavior of the associated tunnel magnetoresistance.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}

@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}
}