Індекс рубрикатора НБУВ: В368.31

Рубрики:

Надпровідність. Надпровідники

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

Thermoelectric effects in a Luttinger liquid (LL) wire adiabatically connected to the leads of noninteracting electrons are considered. For a multichannel LL a staircase-like behavior of the thermal conductance as a function of chemical potential is found. A thermopower for a LL wire with an impurity is evaluated for two cases: (I) LL constriction and (II) infinite LL wire. We show that the thermopower is described a Mott-like formula renormalized by an interaction-dependent factor. For an infinite LL the renormalization factor decreases with increase of the interaction. However, for a realistic situation, when a LL wire is connected to the leads of noninteracting electrons (LL constriction), the repulsive electron-electron interaction enhances the thermopower. A nonlinear Peltier effect in a LL is briefly discussed.

We consider the charge and spin effects in low dimensional superconducting weak links. The first part of the review deals with the effects of electron - electron interaction in Superconductor/Luttinger liquid/Superconductor junctions. The experimental realization of this mesoscopic hybrid system can be the individual single wall carbon nanotube that bridges the gap between two bulk superconductors. The dc Josephson current through a Luttinger liquid is evaluated in the limits of perfectly and poorly transmitting junctions. The relationship between the Josephson effect in a long SNS junction and the Casimir effect is discussed. In the second part of the paper we review the recent results concerning the influence of the Zeeman and Rashba interactions on the thermodynamical properties of ballistic S - QW - S junction fabricated in two dimensional electron gas. It is shown that in magnetically controlled junction there are conditions for resonant Cooper pair transition which results in giant supercurrent through a tunnel junction and a giant magnetic response of a multichannel SNS junction. The supercurrent induced by the joint action of the Zeeman and Rashba interactions in 1D quantum wires connected to bulk superconductors is predicted.

We consider the ectronic properties of empty single-wall nanotubes (SWNT) and SWNT filled with the fullerenle molecules (carbon "nano-peapod"). The first part of the review (section 2) is devoted mostly to the Luttinger liqued properties of individual metallic SWNT coupled to metallic electrodes or to superconducting leads. The discovery of carbon "nano-peapods" and their elastic, electric and thermal properties are reviewed in the second part of the paper (section 3). We suggest in particularly how fullerene and metallofullerene molecules can be raleased from a "nano-peapod" by a purely electrostatic method.

We study theoretically the current-voltage characteristics, shot noise, and full counting statistics of a quantum wire double barrier structure. We model each wire segment by a spinless Luttinger liquid. Within the sequential tunneling approach, we describe the system's dynamics using a master equation. We show that at finite bias the nonequilibrium distribution of plasmons in the central wire segment leads to increased average current, enhanced shot noise, and full counting statistics corresponding to a super-Poissonian process. These effects are particularly pronounced in the strong interaction regime, while in the noninteracting case we recover results obtained earlier using detailed balance arguments.

Superconductivity induced phase-controlled mesoscopic magnetic effects in a two-dimensional electron gas that bridges two superconducting reservoirs are investigated. Giant paramagnetic response of the junction, occuring at certain values of the phase difference of the order parameter, is predicted. A geometrically similar system, consisting of a graphene ribbon stretched between two superconducting leads, is also considered. The magnetic effects in this system are found to be small and the difference between the magnetic properties of the two systems is discussed.

Electron transport through a single-level quantum weakly dot coupled to Luttinger liquid leads is considered in the master equation approach. It is shown that for a weak or moderately strong interaction the differential conductance demonstrates resonant-like behavior as a function of bias and gate voltages. The inelastic channels associated with vibron-assisted electron tunnelling can even dominate electron transport for a certain region of interaction strength. In the limit of strong interaction resonant behavior disappears and the differential conductance scales as a power low on temperature (linear regime) or on bias voltage (nonlinear regime).

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: the persistent current in a circular nanotube, the Josephson current in a nanotube-based SNS junction, and resonant electron tunneling through a chiral nanotube-based quantum dot.

Shuttle-like mechanism of electron transport through a single level vibrating quantum dot is considered in the regime of strong electromechanical coupling. It is shown that the increment of shuttle instability is a nonmonotonic function of the driving voltage. The interplay of two oppositively acting effects - vibron-assisted electron tunneling and polaronic blockade - results in oscillations of the increment on the energy scale of vibron energy.

We considered resonant electron tunneling in various nanostructures including single wall carbon nanotubes, molecular transistors and quantum wires formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron - electron interaction in sequential and resonant electron tunneling are studied by using Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.

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.

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.

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.

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.

A theory of single-electron shuttling in an external magnetic field in nanoelectromechanical system with magnetic leads is presented. We consider partially spin-polarized electrons in the leads and electron transport in both the Coulomb blockade regime and in the limit of large bias voltages when the Coulomb blockade is lifted. The influence of the degree of spin polarization on shuttle instability is considered. It is shown that there is certain degree of spin polarization above which the magnetic field ceases to control electron transport. In the Coulomb blockade regime the dependence of the threshold magnetic field, which separates the "shuttle" and vibron regimes, on the degree of polarization is evaluated. The possibility of re-entrant transitions to the shuttle phase is discussed.

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.

Розглянуто одноелектронний транзистор з тепловим джерелом енергії, який складається з магнітних електродів і рухомого центрального острівця (квантової точки) і знаходиться в зовнішньому магнітному полі. Методом матриці густини вивчено можливість механічної нестійкості в цій системі, яка викликана магнітною обмінною взаємодією між поляризованими за спіном електронами. Аналітично доведено, що у випадку, коли електрони на квантовій точці не взаємодіють, такої механічної нестійкості немає. Для ненульової електрон-електронної взаємодії на квантовій точці чисельно знайдені критичні магнітні поля, що відокремлюють режим механічної нестійкості та електронного шатлювання від режиму механічних коливань, що загасають. Показано, що термоіндуктоване магнітне шатлювання поляризованих за спіном електронів - це порогове явище, і знайдено залежність порогової різниці температур від параметрів системи.

Розглянуто одноелектронний транзистор з тепловим джерелом енергії, який складається з магнітних електродів і рухомого центрального острівця (квантової точки) і знаходиться в зовнішньому магнітному полі. Методом матриці густини вивчено можливість механічної нестійкості в цій системі, яка викликана магнітною обмінною взаємодією між поляризованими за спіном електронами. Аналітично доведено, що у випадку, коли електрони на квантовій точці не взаємодіють, такої механічної нестійкості немає. Для ненульової електрон-електронної взаємодії на квантовій точці чисельно знайдені критичні магнітні поля, що відокремлюють режим механічної нестійкості та електронного шатлювання від режиму механічних коливань, що загасають. Показано, що термоіндуктоване магнітне шатлювання поляризованих за спіном електронів - це порогове явище, і знайдено залежність порогової різниці температур від параметрів системи.