A. E. Plotnikov

Coulomb Blockade and the Thermopower of a Suspended Quantum Dot

On the basis of the 2D electron gas in an AlGaAs/GaAs membrane separated from a wafer, a one-electron transistor is created that operates on the Coulomb blockade effect—a two-barrier structure with a quantum dot. The separation of the sample from the wafer, which has a large dielectric constant, leads to a sharp decrease in the total capacity C of the quantum dot and, as a result, to high charge energy EC = e2/C and critical temperature TC = EC/kB ≈ 40 K. The dependence of the conductance of the quantum dot on the driving and gate voltages includes a rhombic structure characteristic of the Coulomb blockade effect. The phonon-drag thermopower is found in this system. This thermopower exhibits an anomalous alternating dependence on the gate voltage and intensity of the phonon flux. Possible mechanisms are proposed for explaining the indicated anomalies in the thermopower.

Josephson junction arrays on the basis of superconducting PtSi films

Abstract We present the results of low-temperature transport measurements on Josephson junction arrays fabricated on the basis of superconducting polycrystalline PtSi films of thickness 6 nm . To fabricate a two-dimensional array of superconductor—normal-metal–superconductor Josephson weak links, we patterned a square lattice of holes with a period of 600 nm by means of electron lithography and subsequent plasma etching. A periodic variation of the resistance of these arrays with a period corresponding to the magnetic flux quantum per unit cell, including a secondary minimum at the half-quantum points, has been observed.

Blockade of tunneling in a suspended single-electron transistor

The tunneling of electrons that is limited by the Coulomb blockade effect in a single-electron transistor with a quantum dot based on a narrow GaAs/AlGaAs quantum wire suspended over a substrate is investigated. By means of a direct comparison experiment, the tunneling features associated with the separation of the quantum dot from the substrate are revealed. In addition to an increase in the charge energy (Coulomb gap), which reaches 170 K in temperature units, the dependence of this energy on the number of electrons in the quantum dot, which varies from zero to four, is observed. This dependence is explained by a change in the effective size of the dot due to the effect of the depleting gate voltage. Moreover, the additional blockade of tunneling that is different from the Coulomb blockade and is specific for suspended structures is observed. It is shown that this blockade is not associated with the dynamical effect of exciting local phonon modes and can be attributed to the change in the static elastic strains in the quantum wire that accompany the tunneling of an electron to/from the quantum dot.

Anomalous behavior near Tc and synchronization of Andreev reflection in two-dimensional arrays of SNS junctions

The temperature dependences of resistance and the current-voltage characteristics of two-dimensional arrays of superconductor-normal metal-superconductor (SNS) junctions have been measured at low temperatures. It has been found that, in two-dimensional arrays of SNS junctions the following occur: (i) a change in the energy spectrum within an interval of the order of the Thouless energy is observed even when the thermal spread far exceeds the Thouless energy for a single SNS junction; (ii) the manifestation of the subharmonic gap structure with high harmonic numbers is possible even when the energy relaxation length is smaller than that required for the realization of a multiple Andreev reflection in a single SNS junction. These results point to the synchronization of a great number of SNS junctions. A possible mechanism that may be responsible for the features observed in the behavior of two-dimensional arrays of SNS junctions is discussed.

Two-dimensional array of diffusive SNS junctions with high-transparent interfaces

We report a comparative study of the properties of two-dimensional arrays and single superconducting-film--normal-wire--superconducting-film (SNS) junctions. Superconducting and normal metal parts are made from the same material (superconducting polycrystalline PtSi film), ensuring that the NS interfaces of our SNS junctions are highly transparent. We have found the two-dimensional arrays to reveal some unusual features: (i) the significant narrowing of the zero bias anomaly in comparison with single SNS junctions, (ii) the strengthening of subharmonic energy gap structure, with up to

Resonance breakdown of a Coulomb blockade due to the mechanical vibrations of a quantum dot

n=16 (eV=\ifmmode\pm\else\textpm\fi{}2\ensuremath{\Delta}/n),

Giant hysteresis of magnetoresistance in the quantum hall effect regime

with some numbers being lost, (iii) the transition from two-dimensional logarithmic weak localization to metallic behavior. Presented results show that coherent phenomena governed by Andreev reflection are not self-averaging and are maintained over a macroscopic scale.

Nonlinear effects in a two-dimensional electron gas with a periodic lattice of scatterers

The effect of forced mechanical vibrations of a suspended single-electron transistor on Coulomb-blockade limited electron tunneling through a quantum dot has been studied. The mechanical vibrations of the quantum dot have been shown to result in the Coulomb blockade breakdown, which is manifested by narrow resonance peaks of the transistor conductance as a function of the excitation frequency at the frequencies corresponding to the eigenmodes of the mechanical vibrations. The mechanism of the observed effect presumably associated with the oscillations of the mutual electrical capacitances between the quantum dot and the surrounding electrodes is discussed.

Nonequilibrium state of the two-dimensional electron gas in the integer quantum Hall effect regime

A simple system consisting of a two-dimensional electron gas with a narrow conducting wire is studied. In this system, a giant hysteresis of both longitudinal and Hall magnetoresistances in the quantum Hall effect regime is observed for even and odd filling factors v of the Landau levels. At v = 1 and v = 2, the giant hysteresis occurs in the background of the zero-resistance plateau, and the width of the hysteresis loop in a magnetic field is comparable to the plateau width. At the entry to the hysteresis region, the magnetoresistance varies in a threshold manner; i.e., a magnetically induced breakdown of the quantum Hall effect takes place. It is shown that the system under study reflects the relaxation processes in the two-dimensional electron gas adjacent to the wire and, therefore, represents an effective instrument for investigating the hysteresis phenomena in the two-dimensional electron gas itself. An unusual “anticoercive” behavior of the hysteresis is revealed. A comparative analysis of the results obtained and the experimental data on the long relaxation of eddy currents and on the ferromagnetic state of the quantum Hall liquid indicates the common physical origin of these effects.

Transport in one-dimensional electron Sinai billiards

The nonlocal resistance of a two-dimensional electron gas in a periodic lattice of antidots is investigated. Anomalous growth of this resistance is observed when 2Rc≈d (Rc is the Larmor radius). This growth is caused by the appearance of runaway trajectories, skipping along the antidots and running away along the rows of antidots. It is shown on the basis of a comparative analysis of the local and nonlocal magnetoresistance that the character of the electronic billiard trajectories corresponds to the characteristic features of magnetotransport.