I. Ya. Polishchuk

Coulomb correlations and electron-hole liquid in double quantum wells

It has been shown that many-body Coulomb correlations in double quantum wells with spatially separated electrons and holes result in the formation of a degenerate electron-hole liquid where an average distance between the particles is smaller than the size of an isolated exciton. This state turns out to be energetically more favorable than the exciton gas. The results have been obtained under the assumption that there are many different sorts of electrons and holes in the system, which is the case, in particular, in multivalley semiconductors. The relation to the experiments on the observation of luminescent regions in such systems is discussed.

Localization and propagation of phonons in crystals with heavy impurities

Abstract The energy spectrum of a harmonic lattice with heavy impurities is studied within the framework of the scalar model approximation. A detailed analysis of the dynamical properties of the system is made in the frequency range close to the quasi-localized mode. It is shown that the dwell effect for the phonon diffusion coefficient occurs provided the lifetime of the quasi-localized mode becomes of the order of the phonon lifetime. The diffusion coefficient manifests a drastic reduction (the dwell effect) under the same condition necessary for the peak in the heat capacity to be observed. It is shown that the concentration of the impurities needed for observing this effect depends on the impurity mass. For higher concentration of the impurities, the energy gap is shown to appear in the frequency range close to the quasi-local mode. In addition, localized modes are shown to exist in the frequency ranges adjoined to the energy gap.

Complete classification of second-order phase transitions in two-dimensional systems

Abstract A complete classification of second-order phase transitions for two-dimensional systems has been carried out using group-theoretical methods in the framework of the Landau-Lifshits approach. The table presented can be applied for description and prediction of structural second-order phase transitions in monolayer films adsorbed on the surface of crystals. A comparison has been made with experiment.

Low-temperature breakdown of coherent tunneling in amorphous solids induced by the nuclear quadrupole interaction

We consider the effect of the internal nuclear quadrupole interaction on quantum tunneling in complex multi-atomic two-level systems. Two distinct regimes of strong and weak interactions are found. The regimes depend on the relationship between a characteristic energy of the nuclear quadrupole interaction �∗ and a bare tunneling coupling strength �0. When �0 > �∗, the internal interaction is negligible and tunneling remains coherent determined by �0. When �0 < �∗, coherent tunneling breaks down and an effective tunneling amplitude decreases by an exponentially small overlap factor � ∗ ≪ 1 between internal ground states of left and right wells of a tunneling system. This affects thermal and kinetic properties of tunneling systems at low temperatures T < �∗. The theory is applied for interpreting the anomalous behavior of the resonant dielectric susceptibility in amorphous solids at low temperatures T ≤ 5mK where the nuclear quadrupole interaction breaks down coherent tunneling. We suggest the experiments with external magnetic fields to test our predictions and to clarify the internal structure of tunneling systems in amorphous solids.

The long range interaction and the relaxation in glasses at low temperatures

We describe the interaction stimulated relaxation in the ensemble of two-level systems, responsible for low temperature kinetics and thermodynamics properties of amorphous solids. This relaxation gets significant at sufficiently low temperature when phonons are substantially frozen out. We show that in the realistic experimental situation the measuring field strongly accelerates the interaction stimulated relaxation. The characteristic temperature and field dependencies of the relaxation rate are found when the rate is affected both by the interaction between two level systems and by the external field.PACS numbers: 61.43.Fs, 75.50.Lk, 77.22.Ch

Relaxation in glasses at low temperatures

The interaction between tunneling system inherent in amorphous solids is established to be responsible for the universal behavior of their kinetics and thermodynamic properties at low temperature. In this paper, we describe the relaxation mechanism induced by the interaction that falls down as R−3 at large distances. This interaction is either the electrostatic dipole-dipole one or is the elastic one between the point defects (the tunneling system). In the last case, the interaction is due to an indirect interaction induced by acoustic virtual phonon exchange. The relaxation becomes significant at sufficiently low temperature where phonons are substantially frozen out. We show that, in a realistic experimental situation, the measuring field strongly accelerates the interaction-stimulated relaxation. The characteristic temperature and field dependences of the relaxation rate are found when the rate is affected both by the interaction between tunneling systems and by the external field.

Effect of Nuclear Quadrupole Interaction on the Relaxation in Amorphous Solids

Recently it has been experimentally demonstrated that certain glasses display an unexpected magnetic field dependence of the dielectric constant. In particular, the echo technique experiments have shown that the echo amplitude depends on the magnetic field. The analysis of these experiments results in the conclusion that the effect seems to be related to the nuclear degrees of freedom of tunneling systems. The interactions of a nuclear quadrupole electrical moment with the crystal field and of a nuclear magnetic moment with magnetic field transform the two-level tunneling systems inherent in amorphous dielectrics into many-level tunneling systems. The fact that these features show up at temperatures T<100 mK, where the properties of amorphous materials are governed by the long-range R−3 interaction between tunneling systems, suggests that this interaction is responsible for the magnetic field dependent relaxation. We have developed a theory of many-body relaxation in an ensemble of interacting many-level tunneling systems and show that the relaxation rate is controlled by the magnetic field. The results obtained correlate with the available experimental data. Our approach strongly supports the idea that the nuclear quadrupole interaction is just the key for understanding the unusual behavior of glasses in a magnetic field.

Toward a theory of nuclear relaxation in dielectric glasses at ultralow temperatures

The temperature and frequency dependence of the nuclear relaxation rate in dielectric glasses is investigated. It is shown that at low and ultralow temperatures nuclear relaxation is due to an interaction between the nuclear quadrupole moment and fluctuations of the electric field created by dipole moments of two-level systems. Fluctuations of this field can be associated with the background relaxation or are due only to the dipole-dipole interaction between two-level systems. It is shown that at lower temperatures the second relaxation mechanism begins to dominate. Expressions are obtained for the temperature and frequency of crossover between different nuclear relaxation regimes. The possibility of experimental confirmation of our results is discussed.

A self-consistent modeling of the leakage current through thin oxides

A simple computationally effective semi-analytical macroscopic technique of self-consistent calculations of the electrical properties of the MOS structures with ultra thin high-k gate oxide film is developed. Calculated gate voltage - gate leakage [substrate-injected direct and Fowler-Nordheim (FN) tunneling] and gate capacitance characteristics are presented and discussed. The Si/oxide band offset is shown to be the main parameter affecting leakage. The stepwise behaviour of the I - V characteristics is predicted. A contribution of the FN injection is discussed.

Phononless thermal conduction in glasses at ultralow temperatures

It is shown that the thermal conduction in dielectric glasses at ultralow temperatures is provided by energy transfer over the infinite cluster of resonance pairs of two-level systems. Expressions for the phononless thermal conductivity coefficient (∼T4/3) and for the temperature of crossover between the phonon and phononless mechanisms of thermal conduction are obtained. The possibility of experimental corroboration of the results obtained is discussed.