A. A. Gorbatsevich

Toroidal order in crystals

Abstract A new ordered state characterized by non-zero toroidal moment density is described. A review of its electrical and magnetic properties is presented. A second order phase transition to the toroidal state is accompanied by Curie-Weiss behavior of a new type of response function, the toroidal susceptibility, which describes the response to an external current. The toroidal state can be either of spin or of orbital nature. Orbital toroidal magnetics can possess large diamagnetism.

Magnetoelectric phenomena in nanoelectronics

Abstract Two-well quantum structures are considered with broken space inversion and time reversal symmetries. The structures exhibit a number of magnetoelectric phenomena which on microscopic level result from energy spectrum asymmetry in quasimomentum space and from the existence of spontaneous local currents.

Phase separation and dielectric correlations in HTSC

Abstract A general description of the phase separation (PS) in HTSC is presented based on a concept of “soft” dielectric ordering with respect to the addition of collectivized charge carriers. The possibility of the PS crucially depends on the properties of the screening ion subsystem. The interaction of electron and ion subsystems determines a large variety of manifestations of the PS under different experimental conditions. It is shown that the assumption of the existence of the PS makes it possible to explain on common grounds a number of experiments on different HTSC, which seem to be quite separate from each other, such as anomalous magnetoresistance at T T c in Ba 1- x K x BiO 3 , the appearance of midgap states in cuprate HTSC, the existence of two plateaus in the dependence of T c on composition x in YBa 2 Cu 3 O 6+ x , the appearence of photoinduced superconductivity in yttrium superconductors and others.

Magnetoresistance of an asymmetric quantum-size structure in a parallel magnetic field: Field asymmetry independent of the current direction

A new phenomenon, viz., field-asymmetric transverse magnetoresistance of a doped asymmetric quantum-size structure discovered in a magnetic field parallel to the heteroboundary planes, is studied experimentally and theoretically. The magnetoresistance asymmetry relative to the field direction, which is independent of the direction of transport current, is observed when a lateral electric field is embedded in the structure with the help of alloyed metallic contacts. In the theoretical part of the paper, it is shown that the contribution to current, which is asymmetric in the magnetic field, can be consistently described in the framework of the theory of spontaneous current states and photovoltaic effect in systems without an inversion center; the reason behind the emergence of this current is associated with the asymmetry of the energy spectrum of charge carriers relative to the quasimomentum. It is shown that the change in the size and shape of Fermi contours in a magnetic field determines the magnitude of the strong negative magnetoresistance associated with the intersubband scattering under investigation and is found to be responsible for the emergence of a qualitatively new effect mentioned in the title of this paper.

Analogue of gunn effect in tunneling between quantum wells with different mobilities

The electronic transport in a heterostructure with tunnel-coupled quantum wells (QWs) has been studied numerically under conditions of a strongly non-one-dimensional potential in the structure. Current-voltage (I-V) characteristics, potential distribution, and mobility and density of electrons in QWs have been calculated. The numerical technique is based on a two-dimensional consistent calculation of the quantum and classical regions of the heterostructure. The possibility of the occurrence in heterostructures of this kind of an effect similar to the Gunn effect in a homogeneous semiconductor is demonstrated for the first time. The effect is due to electron tunneling between QWs with different mobilities and is characterized by the formation of a high-electric-field domain and the presence of a region of negative differential resistance in the I-V characteristic.

Selfinduced superconducting pairing

Abstract The new mechanism is proposed which describes superconducting pairing in the vicinity of dielectric instability caused solely by interelectron repulsion. The existence of the solution is provided by the self-tuning of the order parameter, possessing different signs in different energy regions. The sign of the order parameter in different momentum regions at fixed energy is fixed, i.e. the solution under consideration is of s-type.

Selfconsistent theory of phase separation in HTSC

Abstract A theory is proposed which explains the phase separation broadly discussed in HTSC as a result of strongly developed dielectric correlations in the electronic subsystem. The self-consistent solution is obtained for the soliton in a system with the essentially none-one dimensional energy spectrum and the criterium is determined for the transition from the periodic-soliton-lattice regime to the phase separation.

The Effect of Structural and Antiferromagnetic Phase Transitions on Superconductivity

Band calculations for La2Cu04 [1] and YBa2Cu307 [2, 3] show that there exists a nesting of Fermi surfaces which seems to be associated with structural (CDW) and antiferromagnetic (SDW) transitions in La2-xMexCu04 [4, 5]. In La2-xMexCu04 the nesting vector corresponds to the dimerization of the period. The observed CDW period, due to the tilting mode, opens a dielectric gap only if the degeneracy of the valence orbitals of the Cu-0 complex [6] is taken into account, contrary to the ordinary Peierls situation.