Manifestation of polaronic effects in Josephson currents

Polaronic effects on the Josephson current through a vibrating quantum dot are considered. In the regime of strong electron–vibron interactions they lead to a power-law suppression of the critical current. This is manifested in an anomalous temperature dependence of the critical current at temperatures of the order of the polaronic energy shift

Nanoelectromechanics of superconducting weak links

Nanoelectromechanical effects in superconducting weak links are considered. Three different superconducting devices are studied: (i) a single-Cooper-pair transistor, (ii) a transparent SNS junction, and (iii) a single-level quantum dot coupled to superconducting electrodes. The electromechanical coupling is due to electrostatic or magnetomotive forces acting on a movable part of the device. It is demonstrated that depending on the frequency of mechanical vibrations the electromechanical coupling could either suppress or enhance the Josephson current. Nonequilibrium effects associated with cooling of the vibrational subsystem or pumping energy into it at low bias voltages are discussed

Superconducting phase-dependent force in SNS junctions with a movable scatterer

We calculate a quantum (Casimir-like) superconducting phase-dependent force acting on a movable scatterer in a superconductor–normal metal–superconductor (SNS) junction. Repulsive Casimir forces are predicted for a short SNS junction with nonequilibrium (inverse) populations of Andreev levels. In a long SNS junction an anomalous (nonmonotonic) temperature behavior of quantum force is found

Low-energy anomalies in electron tunneling through strongly asymmetric Majorana nanowire

Electron transport through Majorana nanowire with strongly asymmetric couplings to normal metal leads is considered. In three terminal geometry (electrically grounded nanowire) it is shown that the presence of unbiased electrode restores zero-bias anomaly even for strong Majorana energy splitting. For effectively two-terminal geometry we show that electrical current through asymmetric Majorana junction is qualitatively different from the analogous current through a resonant (Breit–Wigner) level

Chiral effects in normal and superconducting carbon nanotube-based nanostructures

The novel phenomenon of chiral tunneling in metallic single-wall carbon nanotubes is considered. It is induced by the interplay of electrostatic and pseudomagnetic effects in electron scattering in chiral nanotubes and is characterized by the oscillatory dependence of the electron transmission probability on nanotube chiral angle and the strength of the scattering potential. The appearance of a special (Aharonov–Bohm-like) phase in chiral tunneling affects various phase-coherent phenomena in nanostructures. We considered chiral effects in: (i) the persistent current in a circular nanotube, (ii) the Josephson current in a nanotube-based SNS junction, and (iii) resonant electron tunneling through a chiral nanotube-based quantum dot

Nanomechanics of a magnetic shuttle device

We show that self sustained mechanical vibrations in a model magnetic shuttle device can be driven by both the charge and the spin accumulated on the movable central island of the device. Different scenarios for how spin- and charge-induced shuttle instabilities may develop are discussed and shown to depend on whether there is a Coulomb blockade of tunneling or not. The crucial role of electronic spin flips in a magnetically driven shuttle is established and shown to cause giant magnetoresistance and dynamic magnetostriction effects

Electronic spin working mechanically (Review Article)

A single-electron tunneling (SET) device with a nanoscale central island that can move with respect to the bulk source- and drain electrodes allows for a nanoelectromechanical (NEM) coupling between the electrical current through the device and mechanical vibrations of the island. Although an electromechanical “shuttle” instability and the associated phenomenon of single-electron shuttling were predicted more than 15 years ago, both theoretical and experimental studies of NEM-SET structures are still carried out. New functionalities based on quantum coherence, Coulomb correlations and coherent electron-spin dynamics are of particular current interest. In this article we present a short review of recent activities in this area

Multiterminal open quantum dot circuit operating in the fractional quantum Hall regime

We study theoretically a large quantum dot in the fractional quantum Hall regime that is strongly coupled to M leads via single-mode quantum point contacts. In the case M=2, when the system is mapped onto the two-channel charge Kondo problem, we predict a universal expression for the conductance in the vicinity of a strong-coupling fixed point. The power of the leading temperature correction to the maximal conductance is determined by the fractional filling factor ν=1/m. For M>2, we examine the case in which M-1 quantum point contacts are fully open, reproducing a single-channel circuit coupled to a dissipative Ohmic environment. The system is treated as a Luttinger liquid with an impurity, whose effective interaction parameter is defined as K=ν(M-1)/M. Conductance scaling in the weak and strong tunnel regimes is used to discuss the low-temperature transport behavior of multichannel single- and double-charge Kondo devices. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.11Nscopu

Landau–Zener transitions and Rabi oscillations in a Cooper-pair box: beyond two-level models

We investigate quantum interference effects in a superconducting Cooper-pair box by taking into account the possibility of tunneling processes involving one and two Cooper pairs. The quantum dynamics is analyzed in a framework of three-level model. We compute Landau–Zener probabilities for a linear sweep of the gate charge and investigate Rabi oscillations in a periodically driven three-level system under in- and off-resonance conditions. It was shown that the Landau–Zener probabilities reveal two different patterns: “step”- and “beats”-like behaviors associated with the quantum interference effects. Control on these two regimes is provided by change of the ratio between two characteristic time scales of the problem. We demonstrate through the analysis of a periodically driven three-level system, that if a direct transition between certain pairs of levels is allowed and finetuned to a resonance, the problem is mapped to the two-level Rabi model. If the transition between pair of levels is forbidden, the off-resonance Rabi oscillations involving second order in tunneling processes are predicted. This effect can be observed by measuring a population difference slowly varying in time between the states of the Cooper-pair box characterized by the same parityВивчено квантові інтерференційні ефекти в надпровідному транзисторі з урахуванням можливості тунелювання однієї або двох куперівських пар. Квантову динаміку системи проаналізовано в рамках трирівневої моделі. Розраховано ймовірності Ландау–Зинера в разі лінійної за часом зміни заряду на затворі, а також досліджено осциляції Рабі в трирівневій системи з періодичним накачуванням в умовах резонансу й поза резонансу. Показано, що ймовірності Ландау– Зинера можуть бути розглянуті в двох режимах, що характеризуються ступінчасто- та биттяподібною поведінкою ймовірності. Перехід між режимами здійснюється за допомогою контролю відношення між двома характерними часами в задачі. Продемонстровано, що в трирівневій системи з періодичним накачуванням за умови, коли прямі переходи між певними парами рівнів дозволено, проблема може бути зведена до дворівневої моделі Рабі. У разі, коли прямі переходи між парами рівнів заборонено, передбачено нерезонансні осциляції Рабі, які включають процеси тунелювання другого порядку. Передбачений ефект може бути виявлений за допомогою вимірювання відносної заселеності станів транзистора з тією ж парністю.Изучены квантовые интерференционные эффекты в сверхпроводящем транзисторе с учетом возможности туннелирования одной или двух куперовских пар. Квантовая динамика системы проанализирована в рамках трехуровневой модели. Рассчитаны вероятности Ландау–Зинера в случае линейного по времени изменения заряда на затворе, а также исследованы осцилляции Раби в трехуровневой системе с периодической накачкой в условиях резонанса и вне резонанса. Показано, что вероятности Ландау–Зинера могут быть рассмотрены в двух режимах, характеризуемых ступенчатои биениеподобным поведением вероятности. Переход между режимами осуществляется с помощью контроля отношения между двумя характерными временами в задаче. Продемонстрировано, что в трехуровневой системе с периодической накачкой при условии, когда прямые переходы между определенными парами уровней разрешены, проблема может быть сведена к двухуровневой модели Раби. В случае, когда прямые переходы между парами уровней запрещены, предсказаны нерезонансные осцилляции Раби, которые включают процессы туннелирования второго порядка. Предсказанный эффект может быть обнаружен с помощью измерения относительной заселенности состояний транзистора с той же четностью

Photoinduced anomalous supercurrent Hall effect

We predict a photoinduced Hall effect in an isotropic conventional two-dimensional superconductor with a built-in supercurrent exposed to a circularly polarized light. This second-order with respect to the electromagnetic field amplitude effect occurs when the frequency of the field exceeds double the value of the superconducting gap. It reveals itself in the emergence of a Cooper-pair condensate flow in the direction transverse to the initial built-in supercurrent, which arises to compensate for the light-induced electric current of quasiparticles photoexcited across the gap. The initial supercurrent breaks both the time-reversal and inversion symmetries, while the presence of dilute disorder in the sample provides the breaking of the Galilean invariance. We develop a microscopic theory of the supercurrent Hall effect in the case of weak disorder and show that the Hall supercurrent is directly proportional to the quasiparticle recombination time, which can acquire large values. © 2023 American Physical Society.11Nsciescopu