Работа выполнена в рамках государственного задания России (тема «Спин», № АААА-А18-118020290104-2 и «Электрон», АААА-А18-118020190098-5) при частичной поддержке РФФИ (проект № 17-52-52008) и Правительства Российской Федерации (постановление № 211, контракт № 02.A03.21.0006).
We describe here the study of the Shubnikov–de Haas effect and thermoelectric properties of p-(Bi0.5Sb0.5)2Te3 single crystals doped with Ga, n-Bi2–xTlxSe3 and p-Sb2–xTlxTe3. Using Fourier spectra of the oscillations we calculated the mobility of charge carriers and its variation upon doping. We found that Ga has a donor effect in p-(Bi0.5Sb0.5)2Te3, Tl is an acceptor in n-Bi2–xTlxSe3 and increases the mobility of electrons, while in p-Sb2–xTlxTe3, Tl is a donor and decreases the mobility of holes. We consider the evolution of the defectiveness of crystals that leads to the observed effects. We also synthesized and investigated nanocomposites of solid solutions Sb2Te3–xSex (0 < x < 1). When Se concentration increases in Sb2Te3–xSex, the concentration of holes decreases. At the same time the Seebeck coefficient decreases. This is not typical for semiconductors but correlates with the earlier data. A theoretical model was developed to calculate simultaneously the dependences of the Seebeck coefficient, Hall coefficient and conductivity on the selenium concentration x. Calculations showed that for a simultaneous quantitative description of the thermoelectric and galvanomagnetic data it is necessary to take into consideration both the evolution of the band structure of Sb2Te3–xSex and partial localization of holes.
The in-plane electrical resistivity of single-crystal HoBa2Cu3O7-δ (Tc = 62–66 K) is studied at temperatures Tc–300 K under conditions such that the measurement current flows parallel to twins or at an angle of 45° to them during reversible changes in hydrostatic pressure. The variations in Tc, in the parameters of the Bloch-Grueneisen equations, and in the parameters of the Aslamasov-Larkin model for fluctuation conductivity are analyzed. Application of a pressure facilitates the formation of a second phase with lower Tc that shows up more clearly when the measurement current flows across the twinning plane. In this case, the transverse coherence length and the interval within which the fluctuation conductivity exists are smaller than in the first configuration. The relaxation of the parameters characterizing the scatting of charge carriers on phonons and defects is related to the redistribution of oxygen between the two phases.
Theoretical study of the electrical activity of the saturated superfluid helium (He II) film upon the relative motion of the normal and superfluid components in the film was performed. The polarization vector due to the dipole moments of the quantized vortex rings in He II in the field of van der Waals forces was calculated taking into account the relative motion of the normal and superfluid components. An explicit analytical expression for the electric potential difference arising upon the relative motion of the normal and superfluid components in a torsional oscillator was derived. The obtained time, temperature and relative velocity dependences of the potential difference were in agreement with the experimental data.
Frequencies of the surface electromagnetic states in the photonic crystal–ferrite–plasma-like medium structure were studied both theoretically and experimentally as a function of the ferrite layer thickness, external dc magnetic field and temperature. The photonic crystal was a periodic stack of a finite number of unit cells, each consisting of two different nonmagnetic dielectrics. A nonmagnetic semiconductor played the role of a plasma-like medium. A dc magnetic field was applied parallel to the ferrite layer. The propagation direction of an electromagnetic wave was perpendicular to the dc magnetic field with the electrical component of a microwave field parallel to the magnetic field. An analytical expression relating the frequencies of the surface electromagnetic states to the structural parameters and the magnitude of the dc magnetic field value was derived within the framework of the model of non-conducting and magnetized to saturation ferrite. It was predicted that the states under study are multimodal within a single photonic-crystal band gap.
The mechanisms of stabilization of noncollinear magnetically ordered phases observed in the interval 1.19 <= x <= 1.365 in the Fe{sub 2-x}Mn{sub x}As are considered in the framework of a model approach that uses the information on the number of d-electron and the shape of density of electronic states derived from ab initio calculations. It is found that the energy stability of noncollinear structures and the order of order-order phase transitions depend on electron filling of the d-band and shape of the density of d-electron states, which depend on manganese concentration. It is shown that the baric characteristics of spontaneous and magnetic field induced order-order phase transitions are associated with the nature of renormalization of the electronic structure under pressure.
This is a study of the effect of microstructure created by severe plastic deformation (SPD) and annealing on strain hardening and jump-like deformation in Al-Li alloys. It is shown that under tension at 0.5 K, SPD processed polycrystals retain a significant strain hardening rate and have high strength and ductility. SPD also simulates unstable (jump-like) flow of the polycrystals owing to dislocation dynamics that shows up as stress jumps in the tension curve. The average amplitude of the jumps increases with strain, while the dislocation amplitude distribution corresponds to collective motion of dislocation avalanches with a distinctive scale. Jump-like deformation is partially suppressed by high-temperature annealing, while the distribution of the jump amplitudes is described by a power law. The relationship established between the coefficient of strain hardening and the average stress jump amplitude suggests a common dislocation dynamic for strain hardening and jump-like deformation at low temperatures. The observed features of low-temperature plastic deformation are treated as a consequence of changes in the grain sizes and density of dislocations owing to SPD and annealing.
Igor Yanson showed 38 yr ago for the first time a point-contact measurement where he probed the energy resolved spectroscopy of the electronic scattering inside the metal. Since this first measurement, the point contact spectroscopy (PCS) technique improved enormously. The application of the scanning probe microscopy (SPM) techniques in the late 1980 s allowed achieving contacts with a diameter of a single atom. With the introduction of the mechanically controlled break junction technique, even spectroscopy on freely suspended chains of atoms could be performed. In this paper, we briefly review the current developments of PCS and show recent experiments in advanced scanning PCS based on SPM techniques. We describe some results obtained with both needle-anvil type of point contacts and scanning tunneling microscopy (STM). We also show our first attempt to lift up with a STM a chain of single gold atoms from a Au(110) surface.
The use of Shubnikov-de Haas oscillations for determining effective mass is illustrated by a study of the magnetotransport properties of the two-dimensional hole gas in Si1−xGex (x = 0.13, 0.36, 0.95, 0.98) quantum wells. For some samples the data cannot be fitted to standard theoretical curves in which the scattering of charge carriers is described by the conventional Dingle factor. The reasons for the discrepancies between the experiment the theory are: (i) the effect of spin splitting on the amplitude of the peak in the SdH oscillations; (ii) extra broadening of the Landau levels attributable to an inhomogeneous distribution of the carrier concentration; (iii) the coexistence of short and long-range scattering potentials; and, (iv) population of the second energy level in the quantum well. Ways of calculating the effective hole masses m* for all these cases are presented and values of m* are found for the heterostructures studied here.
The magnetization of FeSe1�xTex x 0, 0.5, and 1.0 compounds has been studied in magnetic fields up to 50 kOe and at temperatures of 2 – 300 K. The superconducting transition was observed at Tc 8 K and 13.6– 14.2 K in FeSe0.963 and FeSe0.5Te0.5, respectively. For most of the samples, nonlinearity of the magnetization curves in the normal state gives evidence of a common, substantial presence of ferromagnetic impurities in these compounds. By taking these impurity effects into account, the intrinsic magnetic susceptibility of FeSe0.963, FeSe0.5Te0.5, and FeTe was estimated to increase gradually with Te content. For FeTe a drastic drop in T with decreasing temperature was found at TN 70 K, which is presumably related to antiferromagnetic ordering. To shed light on the observed magnetic properties, ab initio calculations of the exchange enhanced magnetic susceptibility are performed for FeSe and FeTe in the local spin density approximation. © 2011 American Institute of Physics. doi:10.1063/1.3552132
The previous experience of numerical simulation of superconducting systems is applied to study the behavior of nonstationary wave function far from the equilibrium. It is shown that the normalization of the wave function plays a role of effective nonlocal interaction which leads to a localization of the function in one of the potential valleys even at infinitesimally small difference between deepness of the valleys. This principally differs from the solution of Fokker-Plank equation which exponentially depends on energy and which is practically symmetric for the valleys close in deepness. At a fluctuation change of the deepness relation into the inverse one the maximum of the wave function 'tunnels' from the initial valley into another one. The transition from the excited state a lower one is also studied. It is shown that the transition is accompanied by the emission of a fragment of electromagnetic wave which can be associated with a 'photon'.
molecular transistors and quantum wires formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron–electron interaction in sequential and resonant electron tunneling are studied by using Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed. PACS: 73.63.–b Electronic transport in nanoscale materials and structures; 73.23.Hk Coulomb blockade; single-electron tunneling; 85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices.
Light reflection from the interface of a dielectric film, characterized by a cubic optical nonlinearity, on a bigyrotropic substrate magnetoelectric substrate is investigated theoretically. Relations are obtained for the reflection coefficient as a function of the incidence angle of the light for the main magneto-optic configurations: polar, longitudinal, and transverse. The effect of the magneto-electric and magneto-optical contributions to the electric polarization of such a biaxial structure on the polarization state of the light reflected at angles close to the Brewster angles is studied.
