A new type of quantum size effect in metal-semiconductor superlattices is predicted. Giant oscillations of the transverse tunnel conductivity arise if size quantization of the electron spectrum in the metal layers takes place. This effect is due to the fact that the probability of metal electron tunneling through a semiconductor layer depends sharply on the electron incidence angle. The oscillations have been found to exist even in disordered systems, provided the electrons in metal layers undergo low-angle scattering on imperfections.

Ключ. слова:
Індекс рубрикатора НБУВ: В314.3

Рубрики:

Квантова механіка зіткнень і розсіювання

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

Індекс рубрикатора НБУВ: В368.31

Рубрики:

Надпровідність. Надпровідники

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

Індекс рубрикатора НБУВ: В368.3

Рубрики:

Фізика низьких температур

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

The dc current through a voltage-biased long transparent SNS junction in a dissipative regime is considered. The problem under certain conditions is mapped onto exactly solvable model of energy pumping into a quasiballistic 1D quantum ring driven by time-dependent magnetic flux. A rich peak-like structure of the subgap current at low voltages is predicted. The maxima in the current correspond to resonant energy absorption for fractional values of the normalized bias voltage.

Індекс рубрикатора НБУВ: В368.31

Рубрики:

Надпровідність. Надпровідники

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

We show that quantum spin fluctuations in inhomogeneous conducting ferromagnets drastically affect the Andreev reflection of electrons and holes at a ferromagnet-superconductor interface. As a result, a strong long-range proximity effect appears, associated with electron-hole spin triplet correlations and persisting on a length scale typical for nonmagnetic materials but anomalously large for ferromagnets. For applications, an important consequence is that this long-range proximity effect permits to create superconducting quantum intetference devices with the Josephson magnetic junction of an anomalous large length.

Індекс рубрикатора НБУВ: В378.1

Рубрики:

Теорії металів та металічних сплавів

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

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 transport of spin-polarized electrons through a magnetic single-electron transistor (SET) in the presence of an external magnetic field. Assuming the SET to have a nanometer-sized central island with a single electron level, we find that the zero-frequency shot noise diverges as the on-dot spin-flip rate goes to zero, provided the source and drain leads are completely polarized in the same direction. We present an analytical expression for the low-frequency super-poissonian shot noise that allows one to specify the necessary conditions for the experimental observation of the phenomenon.

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.

Strong coupling between electronic and mechanical degrees of freedom is a basic requirement for the operation of any nanoelectromechanical device. In this Review we consider such devices and in particular investigate the properties of small tunnel-junction nanostructures that contain a movable element in the form of a suspended nanowire. In these systems, electrical currents and charge can be concentrated to small spatial volumes resulting in strong coupling between the mechanics and the charge transport. As a result, a variety of mesoscopic phenomena appear, which can be used for the transduction of electrical currents into mechanical operation. Here we will in particular consider nanoelectromechanical dynamics far from equilibrium and the effect of quantum coherence in both the electronic and mechanical degrees of freedom in the context of both normal and superconducting nanostructures.

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.

We consider a new type of cooling mechanism for a suspended nanowire acting as a weak link between two superconductive electrodes. By applying a bias voltage over the system, we show that the system can be viewed as a refrigerator for the nanomechanical vibrations, where energy is continuously transferred from the vibrational degrees of freedom to the extended quasiparticle states in the leads through the periodic modulation of the inter-Andreev level separation. The necessary coupling between the electronic and mechanical degrees of freedom responsible for this energy-transfer can be achieved both with an external magnetic or electrical field, and is shown to lead to an effective cooling of the vibrating nanowire. Using realistic parameters for a suspended nanowire in the form of a metallic carbon nanotube we analyze the evolution of the density matrix and demonstrate the possibility to cool the system down to a stationary vibron population of ~ 0,1. Furthermore, it is shown that the stationary occupancy of the vibrational modes of the nanowire can be directly probed from the dc current responsible for carrying away the absorbed energy from the vibrating nanowire.

We investigate resonant interaction of conduction electrons with an electromagnetic field that irradiates a point contact between a ferromagnetic and a normal metal in the presence of a strong magnetic field of order 1 T. We show that electron spin-flips caused by resonant absorption and stimulated emission of photons result in a sharp peak in the magnetic-field dependence of the point-contact resistance. The height of the peak is shown to be directly proportional to the net rate of energy transfer to the electromagnetic field in the point contact due to absorption and stimulated emission of photons. Estimations indicate that our theory can serve as a basis for the explanation of recent experiments [A. M. Kadigrobov et al., New J. Phys. 13, 023007 (2011)].

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.

Індекс рубрикатора НБУВ: В377.3

Рубрики:

Магнітні властивості твердих тіл. Магнетики

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

We show theoretically that a significant spin accumulation can occur in electric point contacts between two ferromagnetic electrodes with different magnetizations. Under appropriate conditions an inverse population of spin-split electronic levels results in stimulated emission of photons in the presence of a resonant electromagnetic field. The intensity of the emitted radiation can be several orders of magnitude higher than in typical semiconductor laser materials for two reasons. The density of conduction electrons in a metal point conduct is much larger than in semiconductors. The strength of the coupling between the electron spins and the electromagnetic field that is responsible for the radiative spin-flip transitions is set by the magnetic exchange energy and can therefore be very large as suggested by Kadigrobov et al. [Europhys. Lett. 67, 948 (2004)].