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.

The magnetotransport in a two-dimensional electron gas with a lattice of antidots, which has a record-breaking small (80 nm) period and size (20–40 nm) of antidots comparable with the de Broglie wavelength of electrons, has been experimentally studied. A wide variety of new features of the magnetoresistance behavior has been observed both under semiclassical conditions and in the regime of quantizing magnetic fields. In particular, the anomalous semiclassical magnetoresistance peak induced by the nonmonotonic scattering effects has been revealed. The Shubnikov-de Haas oscillations have been revealed to exhibit an unusual transition from the anomalous period constant in the magnetic field to the normal constant in the inverse magnetic field. The effect of the generation and suppression of the oscillations has also been observed; this effect is induced by the transformation of the short and long-range scattering potentials in the lattice owing to the variation of the density of the two-dimensional electrons.

Commensurate peaks of magnetoresistance and Shubnikov-de Haas and Aharonov-Bohm oscillations in the two-dimensional electron gas (2DEG) in a lattice of antidots with hard potential walls have been experimentally studied. The behavior of both classical magnetoresistance peaks and quantum oscillations has been shown to fundamentally depend on the lattice period and the antidot size, as well as on the smoothness of the potential at the 2DEG-antidot interface. This result indicates the necessity of revising the interpretation of all numerous experiments with antidot lattices, since this effect has been explicitly or implicitly neglected in them.

We have compared the properties of the nonequilibrium state of the two-dimensional electron gas observed in the samples of different types by means of magnetotransport and magnetization measurements in the quantum Hall effect regime at integer filling factors n . It has been found that the range of filling factors corresponding to the nonequilibrium state is universal for the samples of different types and different measurement techniques and varies from 0.1 to 0.3 for n changing from 1 to 4. The comparison indicates that the observed nonequilibrium state is not directly caused by the appearance of eddy currents and the dielectric phase in the two-dimensional electron gas but is probably associated with the magnetic field-induced phase transition.

Influence of forced mechanical vibrations of a suspended single-electron transistor on electron tunneling through the quantum dot limited by the Coulomb blockade is investigated. It is shown that mechanical oscillations of the quantum dot lead to the Coulomb blockade breakdown, shown in sharp resonant peaks in the transistor conductance dependence on the excitation frequency at values corresponding to the mechanical oscillations eigen modes. Physical mechanism of the observed effect is considered. It is presumably connected with oscillations of the mutual electrical capacitances between the quantum dot and surrounding electrodes.

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.

We report on the observation of ultra-high Aharonov–Bohm oscillations harmonics h/ne (n=40–45) in a very small quasibalistic ring (the ring effective radius is r=60–75nm) fabricated on the basis of AlGaAs/GaAs heterostructures with a 2D electron gas. The highest harmonics observed so far were n=2–4. The observation of harmonics of so high a frequency proves that in real scattering systems with dimensions of the order of the electron wave-length, multiple back-scattering processes are quite common.

The conductance of short ballistic wires with boundaries, whose curvature radius is comparable to the electron wavelength, is investigated. It is found that, in such wires, no conductance quantization takes place. Instead, pronounced interference effects are observed. These effects are related to the Fabry-Perot interference by the wire edges and with the mesoscopic interference caused by the coherent scattering of electrons by the wire edges and by the impurities located in the near-wire regions of the 2D electron gas.

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.

We study the magnetic field dependence of the resistance of ultrathin superconducting PtSi films perforated with a square pattern of holes with a period of 500nm forming a lattice of constrictions connected by islands of the film. At temperatures below the superconducting critical temperature of the islands, the magnetoresistance oscillations with a period of one flux (h/2e) per lattice cell have been clearly observed. However, in the critical region between the temperature of Berezinskii–Kosterlitz–Thouless transition and the mean field BCS transition temperature the oscillations are superimposed on a background of negative magnetoresistance in weak magnetic field. Careful analysis of the shape of the oscillations shows that they are a superposition of h/2e and h/4e oscillations. The observation of h/4e period of Aharonov–Bohm oscillations simultaneously with a negative magnetoresistance supports the prediction that correlation effects can produce a negative Josephson coupling in a disordered superconductor.

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 E C = e 2/C and critical temperature T C = E C/k B ≈ 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.

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.

Commensurability oscillations of thermopower in a square antidot lattice are observed. The oscillations are attributed to the geometrical resonances of the classical electron motion in a magnetic field and are much more pronounced than the corresponding magnetoresistance oscillations. The off-diagonal component of the thermopower tensor (the Nernst-Ettingshausen effect) changes sign at resonances. Additional measurements of magnetoresistance verify the correctness of the method used for thermopower measurements and provide information on the temperature distribution in the sample.

An experimental study of the two-, three-, and four-terminal resistance of a ballistic wire is carried out. The wire is fabricated on the basis of high-mobility 2D electron gas in an AlGaAs/GaAs heterojunction. Different behavior of mesoscopic fluctuations of multiterminal resistances is observed depending on the gate voltage and magnetic field. At B=0.45 T, the four-terminal resistance drops almost to zero and features resembling a ballistic conductance quantization are observed.

The mesoscopic fluctuations of thermopower (MFT) were experimentally observed in an AlGaAs/GaAs heterojunction with a low-resistance (∼0.02 h / e 2 ) periodic antidot lattice in the situation where the mesoscopic fluctuations of conductance (MFC) were absent to within the experimental accuracy. The MFT spectrum contained a periodic component associated with the Aharonov-Bohm h / e oscillations in the area occupied by one antidot, whereas the h /2 e oscillations were not observed. It is shown that a sizable contribution to the MFT comes from the interference of electron trajectories localized inside billiards formed by four neighboring antidots. Contrary to MFC, the MFT autocorrelation function in single billiards deviates from the Lorentzian form.

We present the results of low-temperature transport measurements on Josephson junction arrays fabricated on the basis of superconducting polycrystalline PtSi films of thickness 6nm. 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 600nm 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.

Magnetotransport in a ballistic wire under the conditions of integer and fractional quantization was studied experimentally. A nonlinear magnetic-field dependence of filling factor (ν) of the Landau level was observed; this dependence arises if the self-consistent electrostatic potential of the wire has a specific form. It is assumed that the observed effect results from the influence of interaction between electrons at the partially occupied Landau level on this potential, which brings about a decrease in the electron concentration in the wire as the magnetic field increases in the case of ν<1.

The thermopower of a multiprobe ballistic conductor in the form of caterpillarlike Sinai billiard is experimentally investigated. The magnetic-field dependence of both longitudinal thermopower and Nernst-Ettingshausen effect exhibits commensurability oscillations, which are more pronounced than the corresponding oscillations in the magnetoresistance. Results of computer calculations based on the generalized Landauer-Buttiker approach are in agreement with experiment. The observed features in the thermopower originate from drastic difference between the transmission coefficients of quasielectrons (above the Fermi level) and quasiholes (below the Fermi level) in the vicinity of geometrical resonances.

Thermopower of a solid-state caterpillar Sinai billiard is experimentally investigated. Observed commensurability oscillations of magnetothermopower are much more pronounced than those of magnetoresistance. The magnetothermopower anomalies are adequately described by the Mott formula for the hard-wall billiard model. Computer simulation of a map, relating initial conditions of electrons, injected into the billiard to corresponding outgoing probe, has made it possible to reveal specific trajectories responsible for the observed features.

The behavior of the weak localization (WL) in a dense hexagonal lattice of antidots is investigated. The WL can be described by the usual law for disordered conductors using an additional prefactor a. The phase coherence length L, and a were obtained through a fit of the WL, revealing specific features in the amplitude of the WL. Finally the universal scaling function beta = d ln sigma /d lnL(psi) was obtained, The beta (ln sigma) dependence was found to be non-universal and nonmonotonic. This result contradicts the one parameter scaling theory of localization.