MICROWAVE-INDUCED RESONANT REFLECTION AND LOCALIZATION OF BALLISTIC ELECTRONS IN QUANTUM MICROCHANNELS

We show that electron transport in a ballistic microchannel supporting both propagating and reflected modes can be completely blocked by applying a microwave electromagnetic field. The effect is due to resonant reflection caused by multiple coherent electron-photon scattering involving at least two spatially localized scattering centers in the channel. With many such scattering centers present the conductance is shown to have an irregular dependence on bias voltage, gate voltage and frequency with irregularily spaced dips corresponding to resonant reflection. When averaged over bias, gate voltage or frequency the conductance will decay exponentially with channel length in full analogy with the localization of 1D electrons caused by impurity scattering.Comment: 4 pages, latex, 1 figure available on reques

Igor Orestovich Kulik To the 75th birthday anniversary

Igor Orestovich Kulik — a prominent physicist and an outstanding representative of Kharkov’s school of theoretical physics, Corresponding member of the National Academy of Sciences of Ukraine and Ukrainian State Prize Laureate — will be 75 on November 19 this year

Influence of dissipation on a low-voltage dc current in a long SNS junction

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

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

Dynamics of current induced magnetic superstructures in exchange-spring devices

Thermoelectric manipulation of the magnetization of a magnetic layered stack in which a low-Curie temperature magnet is sandwiched between two strong magnets (exchange spring device) is considered. Controllable Joule heating produced by a current flowing in the plane of the magnetic stack (CIP configuration) induces a spatial magnetic and thermal structure along the current flow — a magnetothermal-electric domain (soliton). We show that such a structure can experience oscillatory in time dynamics if the magnetic stack is incorporated into an electric circuit in series with an inductor. The excitation of these magnetothermionic oscillations follow the scenario either of “soft” of “hard” instability: in the latter case oscillations arise if the initial perturbation is large enough. The frequency of the temporal oscillations is of the order of 10⁵–10⁷ s⁻¹ for current densities j ~ 10⁶ –10⁷ A/cm²

Novel laser based on magnetic tunneling

A new principle for a compact spin-based solid-state laser is proposed. It operates in the 1–100 THz regime, which is difficult to reach with small size lasers. Spin-flip processes in ferromagnetic conductors form a basis — the mechanism is due to a coupling of light to the exchange interaction in magnetically ordered conductors via the dependence of the exchange constant on the conduction electron momenta. The interaction strength is proportional to the large exchange energy and exceeds the Zeeman interaction by orders of magnitude. A giant lasing effect is predicted in a system where a population inversion has been created by injection of spin-polarized electrons from one ferromagnetic conductor into another through an intermediate tunnel region or weak link; the magnetizations of the two ferromagnets have different orientations. We show that the laser frequency will be in the range 1–100 THz if the experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization are used. The optical gain is estimated to be gopt ~ 10⁷ cm⁻¹. This exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. An experimental configuration is proposed in order to solve heating problems at a relatively high threshold current density

Graphene and graphene-based nanostructures

This issue of the journal «Fizika Nizkikh Temperatur» is dedicated to the discovery of graphene — a monolayer graphite — in 2004

Coherent quantum phenomena in a normal cylindrical conductor with a superconducting coating

The thermodynamic properties of a mesoscopic-size, simply connected cylindrical normal metal in good metallic contact with superconducting banks are studied theoretically. It is commonly accepted that if the superconductor thickness is quite small (of the order of the coherence length), as is assumed to be the case here, a vector potential field, whose value can be varied, exists inside the normal layer. It is further assumed that the quasiparticles with energy E<Δ (2Δ is the superconducting gap) move ballistically through the normal metal and undergo Andreev scattering caused by the off-diagonal potential of the superconductor. An equation is obtained within the multidimensional quasiclassical method which permits us to determine the spectrum of the Andreev levels and to calculate the density of states of the system in question. It is shown that the Andreev levels shift as the trapped flux Φ changes inside the normal conductor. At a certain flux value they coincide with the Fermi level. A resonance spike in the density of states ν(E) appears in this case, since near E=0 there is strong degeneracy of the quasiparticle states in respect to the quantum number q characterizing their motion along the cylinder axis. As a result, a macroscopic number of q states contribute to the amplitude of the effect. As the flux is increased, the density of states v(E) behaves as a stepwise function of Φ. The distance between the steps is equal to the superconducting flux quantum hc/2e

Carbon «peapods» – a new tunable nanoscale graphitic structure (Review Article)

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

Photon generation in ferromagnetic point contacts

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. (1) The density of conduction electrons in a metal point conduct is much larger than in semiconductors. (2) 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)]