@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}
}