arXiv subjects

S. N. Shevchenko

Publications and source records attributed to S. N. Shevchenko.

48 records · Page 3Linked to original sources

arXiv2005

Multiphoton transitions between energy levels in a phase-biased Cooper-pair box

We investigated both theoretically and experimentally dynamic features of a phase-biased charge qubit consisting of a single-Cooper-pair transistor closed by a superconducting loop. The effective inductance of the qubit was probed by a high-quality tank circuit. In the presence of a microwave power, with a frequency of the order of the qubit energy level separation, an alteration of the qubit inductance was observed. We demonstrate that this effect is caused by the redistribution of the qubit level population. The excitation of the qubit by one-, two-, and three-photon processes was detected. Quantitative agreement between theory and experimental data was found.

cond-mat.supr-con↗

arXiv2005

Josephson effect in a weak link between borocarbides

A stationary Josephson effect is analyzed theoretically for a weak link between borocarbide superconductors. It is shown that different models of the order parameter result in qualitatively different current-phase relations.

cond-mat.supr-con↗

arXiv2005

Conductance of the elliptically shaped quantum wire

The conductance of a ballistic elliptically shaped quantum wire is investigated theoretically. It is shown that the effect of the curvature results in strong oscillating dependence of the conductance on the applied bias.

cond-mat.mes-hall↗

arXiv2005

Vortex-like current states in Josephson ballistic point contacts

The stationary Josephson effect is studied theoretically in the situation when there is externally injected transport supercurrent which flows in the banks parallel to the contact interface. Coexistence of this supercurrent with the order parameter phase difference between the banks of the contact results in the appearance of quasiparticles in the weak link, which create the current, localized in the vicinity of the contact and counter-flowing to the transport supercurrent. We review the results of our previous study of weak links between current-carrying conventional and unconventional (d-wave) superconductors. And further we study the weak link in the form of double point contact between current-carrying superconductors. The current distribution patterns, containing the vortex-like states, are obtained.

cond-mat.supr-con↗

arXiv2005

Hyperfine-driven persistent currents in mesoscopic rings based on a 2D electron gas with Rashba spin-orbit interaction

We present a detailed theory of induced persistent current produced by hyperfine interaction in mesoscopic rings based on a 2D-electron (hole) gas in the absence of external magnetic field. The persistent current emerges due to combined action of the hyperfine interaction of charge carriers with polarized nuclei, spin-orbit interaction and Berry phase.

cond-mat.mes-hall↗

arXiv2004

Dynamic behaviour of Josephson-junction qubits: crossover between Rabi oscillations and Landau-Zener transitions

We study the dynamic behaviour of a quantum two-level system with periodically varying parameters by solving the master equation for the density matrix. Two limiting cases are considered: multiphoton Rabi oscillations and Landau-Zener transitions. The approach is applied to the description of the dynamics of superconducting qubits. In particular, the case of the interferometer-type charge qubit with periodically varying parameters (gate voltage or magnetic flux) is investigated. The time-averaged energy level populations are calculated as funtions of the qubit's control parameters.

cond-mat.supr-con↗

arXiv2004

Impact of the transport supercurrent on the Josephson effect

We study the weak link between current-carrying superconductors, both conventional and d-wave. The state of the system is controlled by two parameters: the order parameter phase difference $ϕ$ and the superfluid velocity $v_{s}$, which parameterizes the parallel to the boundary transport supercurrent which is injected externally. The low-temperature current-phase relations are derived. We consider two models of weak links: a constriction between two conventional superconductors and a plane boundary between two differently orientated d-wave superconductors. We show that for some relation between $ϕ$ and $v_{s}$ quasiparticles create the current along the boundary which flows in the direction opposite to the transport supercurrent.

cond-mat.supr-con↗

arXiv2003

Josephson and spontaneous currents at the interface between two d-wave superconductors with transport current in the banks

A stationary Josephson effect in the ballistic contact of two d-wave superconductors with different axes orientation and with tangential transport current in the banks is considered theoretically. We study the influence of the transport current on the current-phase dependence for the Josephson and tangential currents at the interface. It is demonstrated that the spontaneous surface current at the interface depends on the transport current in the banks due to the interference of the angle-dependent current-carrying condensate wave functions of the two superconductors.

cond-mat.supr-con↗

arXiv2003

Magnetization of Nuclear-Spin-Polarization-Induced Quantum Ring

Properties of a Nuclear-Spin-Polarization-Induced Quantum Ring (NSPI QR) are studied theoretically. In the proposed system a local nuclear spin polarization creates an effective hyperfine field which confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear spin polarization. We investigate the electron energy spectrum and the magnetic response of NSPI QR and their evolution in time due to the nuclear spin diffusion and relaxation.

cond-mat.mes-hall↗

arXiv2003

Nonlocal mixing of supercurrents in Josephson ballistic point contact

We study coherent current states in the mesoscopic superconducting weak link simultaneously subjected to the order parameter phase difference on the contact and to the tangential to the junction interface superfluid velocity in the banks. The Josephson current-phase relation controlled by the external transport current is obtained. At phase difference close to pi the nonlocal nature of the Josephson phase-dependent current results in the appearance of two vortexlike states in the vicinity of the contact.

cond-mat.supr-con↗

arXiv2003

Electronic transport through nuclear-spin-polarization-induced quantum wire

Electron transport in a new low-dimensional structure - the nuclear spin polarization induced quantum wire (NSPI QW) is theoretically studied. In the proposed system the local nuclear spin polarization creates the effective hyperfine field which confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear spin polarization. The influence of the nuclear spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed.

cond-mat.mes-hall↗

arXiv2002

Josephson effect in point contacts between ''f-wave'' superconductors

A stationary Josephson effect in point contacts between triplet superconductors is analyzed theoretically for most probable models of the order parameter in UPt_{3} and Sr_{2}RuO_{4}. The consequence of misorientation of crystals in superconducting banks on this effect is considered. We show that different models for the order parameter lead to quite different current-phase dependences. For certain angles of misorientation a boundary between superconductors can generate the parallel to surface spontaneous current. In a number of cases the state with a zero Josephson current and minimum of the free energy corresponds to a spontaneous phase difference. This phase difference depends on the misorientation angle and may possess any value. We conclude that experimental investigations of the current-phase dependences of small junctions can be used for determination of the order parameter symmetry in the mentioned above superconductors.

cond-mat.supr-con↗