Gravitational Instability of a Rotating Viscous Finitely Conducting Plasma

The gravitational instability of infinite homogeneous plasma has been studied to include simultaneously the effects of rotations, Hall currents, viscosity, finite electrical conductivity and the finite Larmor radius (FLR). Both the longitudinal, and transverse modes of wave propagation have been studied. It is found that the gravitational instability is determined by Jeans' criterion even in the presence of effects of rotation, Hall currents, FLR, viscosity and finite conductivity whether included separately or jointly.     

Gravitational Instability of a Rotating Viscous Thermally Conducting Plasma

This paper deals with the gravitational instability of an infinite homogeneous viscous rotating plasma of finite electrical conductivity in the combined presence of effects of Hall currents, finite Larmor radius (FLR) and thermal conductivity. The ambient magnetic field is assumed to be uniform and acting along the vertical direction. Both longitudinal and transverse modes of wave propagation have been studied. It is shown that Jean's criterion determines the gravitational instability even in the presence of the effects of thermal conductivity, viscosity, finite electrical conductivity, FLR, rotation and Hall currents. Further it is found that while FLR, viscosity and rotation have a stabilizing influence, both the thermal and the electrical conductivities have a destabilizing influence on the gravitational instability of a plasma.     

Gravitational Instability of a Thermally Conducting Plasma in an Oblique Magnetic Field

The combined influence of the effects of Hall currents, magnetic resistivity and viscosity have been studied on the gravitational instability of a thermally conducting homogeneous unbounded plasma in an oblique magnetic field. The solution has been obtained through the normal mode technique and the dispersion relation has been derived. It is shown that the Jeans' criterion for gravitational instability remains unchanged. Solving numerically the dispersion relation, the dependence of the growth rate of the gravitational unstable mode on the considered physical effects has been obtained for an astrophysical situation. For conditions prevailing in the magnetized collapsing clouds, the numerical calculations for the plot of growth rate against wave number has been obtained for several values of the parameters characterizing Hall currents magnetic resistivity viscosity thermal conductivity. It is found that magnetic resistivity and thermal conductivity have destabilizing influence while viscosity has stabilizing influence on the instability of the plasma of disturbance m(ϱ) = 9 × 10⁻³ kg.     

Basic types of nonuniformities and their manifestation in the galvanomagnetic properties of especially pure silicon

A method is proposed for analyzing the type of nonuniformities in a single-crystalline pure material based on the changes in the asymmetry resistances, determined from the magnitudes of the external potentials on the Hall contacts, in a magnetic field. By comparing their magnetic-field dependences with the analogous dependences of the Hall constant and of the resistivity, measured with different polarities of the voltage applied to the sample, it is shown that the asymmetry resistances are the parameters which are most sensitive to nonuniformity. It was found that nonuniformities of the compensation type, i.e., space-charge regions in which the minority carriers make an appreciable contribution to the Hall constant, are systematically manifested in crystals of especially pure high-resistance silicon. The effective Hall factors were calculated under the conditions of Hall bipolarity of the impurity conductivity and the results are compared with the experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 63–76, June, 1987.     

Properties of liquid PbS,PbSe and PbTe

We present here a study of the various properties of liquid PbS, PbSe and PbTe. In the first part of the presentation, we discuss the various possible models in the light of the semiconducting properties of these liquids. The electrical conductivity studies lead us to believe that the temperature dependence of electrical conductivity for these liquids is in accord with our earlier reported⁽¹⁾ studies of the temperature dependence of the energy gap for crystalline PbS, PbSe and PbTe. We also give an interpretation for σ₀, and discussion of the Hall coefficient and the Hall mobility is presented. The next part of the presentation deals with thermal conductivity, thermoelectric power and other related properties. The negative values of the thermoelectric power for these liquids are qualitatively analysed. Our studies of the magnetic susceptibility for crystalline and liquid PbTe indicate that the ratio of the transition term to the energy gap is a constant at all temperatures so that the Van-Vleck component is temperature independent, thereby explaining the constancy of the total susceptibility. Electronegativity and ionicity studies are presented. Finally, we report our studies of the density, viscosity and other physio-chemical properties.     

The conductivity of a two-dimensional electronic system of finite width in the presence of a strong perpendicular magnetic field and a random potential

Starting from the Kubo formula the conductivity tensor of a two-dimensional electronic system in a perpendicular magnetic field is evaluated. It is shown that at zero temperature only the states at the Fermi level contribute. The Hall conductivity of a purely periodic system of finite width is calculated and compared with earlier suggestions by Thouless et al. For a system described by a periodic and a random potential the Hall conductivity is calculated as a function of the electron density. The results emphasize the importance of disorder independent current carrying states for the Quantum Hall effect which extend along the boundaries of the system. The plateaux values of the Hall conductivity are related to the number of these states, and are independent of the existence of extended bulk states below the Fermi energy.     

Jeans' gravitational instability of a thermally conducting plasma

The gravitational instability of an infinitely extending homogenous plasma endowed with several physical mechanisms, namely Hall currents, finite conductivity, ion viscosity and thermal conductivity is considered. The main result is that the various parameters play different physical roles in the perturbed problem. Jeans' criterion is analyzed in the framework of Tsallis' statistics for possible modifications due to the presence of nonextensive effects. A simple generalization of the Jeans' criterion is obtained and the standard values are obtained in the limiting case q=1, q being the nonextensive parameter.     

Hall Conductivity in the Cosmic Defect and Dislocation Spacetime

Influences of topological defect and dislocation on conductivity behavior of charge carriers in external electromagnetic fields are studied.Particularly the quantum Hall effect is investigated in detail.It is found that the nontrivial deformations of spacetime due to topological defect and dislocation produce an eiectric current at the leading order of perturbation theory.This current then induces a deformation on the Hall conductivity.The corrections on the Hall conductivity depend on the external electric fields,the size of the sample and the momentum of the particle.     

Vertex corrections to the anomalous Hall effect in spin-polarized two-dimensional electron gases with a Rashba spin-orbit interaction

We study the effect of disorder on the intrinsic anomalous Hall conductivity in a magnetic two-dimensional electron gas with a Rashba-type spin-orbit interaction. We find that anomalous Hall conductivity vanishes unless the lifetime is spin-dependent, similar to the spin Hall conductivity in the nonmagnetic system. In addition, we find that the spin Hall conductivity does not vanish in the presence of magnetic scatterers.     

Gap opening in the zeroth Landau level in gapped graphene: pseudo-Zeeman splitting in an angular magnetic field

We present a theoretical study of gap opening in the zeroth Landau level in gapped graphene as a result of pseudo-Zeeman interaction. The applied magnetic field couples with the valley pseudospin degree of freedom of the charge carriers leading to the pseudo-Zeeman interaction. To investigate its role in transport at the charge neutrality point (CNP), we study the integer quantum Hall effect in gapped graphene in an angular magnetic field in the presence of pseudo-Zeeman interaction. Analytical expressions are derived for the Hall conductivity using the Kubo-Greenwood formula. We also determine the longitudinal conductivity for elastic impurity scattering in the first Born approximation. We show that pseudo-Zeeman splitting leads to a minimum in the collisional conductivity at high magnetic fields and a zero plateau in the Hall conductivity. Evidence for activated transport at CNP is found from the temperature dependence of the collisional conductivity.     

Electric- and magnetic-field-tuned Landau levels and Hall conductivity in AA-stacked bilayer graphene

We theoretically study the combined effect of magnetic and electric fields on the Landau levels and Hall conductivity in AA-stacked bilayer graphene. From the analytic expressions derived, we obtain explicit criterions for determining the zero-energy Landau level and different level crossings in the graphene bilayer. For providing a scheme of experimental verification, we further explore the quantum Hall effect in such a biased bilayer. It is found that the zero-conductance Hall plateau in this system can vanish at certain specific combinations of magnetic and electric fields, accompanying with the occurrence of resonance Hall conductivity steps.     

Bound values for Hall conductivity of heterogeneous medium under quantum Hall effect conditions

Bound values for Hall conductivity under quantum Hall effect (QHE) conditions in inhomogeneous medium has been studied. It is shown that bound values for Hall conductivity differ from bound values for metallic conductivity. This is due to the unusual character of current percolation under quantum Hall effect conditions.      

Anomalous Hall effect of heavy holes in III-V semiconductor quantum wells

The anomalous Hall effect of heavy holes in semiconductor quantum wells is studied in the intrinsic transport regime, where the Berry curvature governs the Hall current properties. Based on the first--order perturbation of wave function the expression of the Hall conductivity the same as that from the semiclassical equation of motion of the Bloch particles is derived. The dependence of Hall conductivity on the system parameters is shown. The amplitude of Hall conductivity is found to be balanced by a competition between the Zeeman splitting and the spin--orbit splitting.     

Comments on the equilibrium theory of the quantum hall effect

The relation between the thermal equilibrium Hall conductivity generated by minimal gauge transformation and the isolated Hall conductivity given by the Kubo formula is investigated. The contribution of the edge states and some general questions concerning the definition of the equilibrium Hall conductivity are discussed. It is shown that, in the case of an additive electron-impurity system, the two Hall conductivities coincide as long as the Fermi energy is situated in an energy gap.     

Linear magnetization dependence of the intrinsic anomalous Hall effect

The anomalous Hall effect is investigated experimentally and theoretically for ferromagnetic thin films of Mn5Ge3. We have separated the intrinsic and extrinsic contributions to the experimental anomalous Hall effect and calculated the intrinsic anomalous Hall conductivity from the Berry curvature of the Bloch states using first-principles methods. The intrinsic anomalous Hall conductivity depends linearly on the magnetization, which can be understood from the long-wavelength fluctuations of the spin orientation at finite temperatures. The quantitative agreement between theory and experiment is remarkably good, not only near 0 K but also at finite temperatures, up to about approximately 240 K (0.8TC).     

Ab initio calculation of the intrinsic spin Hall effect in semiconductors

Relativistic band theoretical calculations reveal that intrinsic spin Hall conductivity in hole-doped archetypical semiconductors Ge, GaAs, and AlAs is large [approximately 100(planck/e)(Omega cm)(-1)], showing the possibility of a spin Hall effect beyond the four-band Luttinger Hamiltonian. The calculated orbital-angular-momentum (orbital) Hall conductivity is one order of magnitude smaller, indicating no cancellation between the spin and orbital Hall effects in bulk semiconductors. Furthermore, it is found that the spin Hall effect can be strongly manipulated by strains, and that the ac spin Hall conductivity is large in pure as well as doped semiconductors.     

Hall Currents and the Rayleigh-Taylor Instability of a Finitely Conducting Plasma in the Presence of Coriolis Forces

We have studied the effect of rotation on the development of Rayleigh-Taylor instability of an incompressible, viscous, Hall, finitely conducting plasma of variable density. The solution is developed, through variational methods, for a semi-infinite plasma in which the density varies exponentially along the vertical. It is found that the system is unstable for all wave numbers when the effects of magnetic resistivity are included. The effects of coriolis forces and viscosity on the growth rate of the unstable system are found to be stabilizing while that of Hall currents is destabilizing. Finite conductivity affects the growth rate of the unstable mode differently for the smaller and larger values of the wave numbers, destabilizing for the waves of large wave length and stabilizing for waves of small wave length.     

Bound values for Hall conductivity and percolation under quantum Hall effect conditions

The percolation under Quantum Hall Effect conditions in inhomogeneous medium has been studied. The lower and upper bound possible values for effective Hall conductivity values have been established. It has been shown that these bound values for Hall conductivity differ from bound values for metal conductivity. It comes from unusual character of current percolation under Quantum Hall Effect conditions. The physical sense of obtained results has been discussed.     

Screw dislocation-induced influence of transverse modes on Hall conductivity

The Hall conductivity of an electron gas on an interface showing a topological defectcalled screw dislocation is investigated. This kind of defect induces a singular torsionon the medium which in turn induces transverse modes in the quantum Hall effect. It isshown that this topology decreases the plateaus’ widths and shifts the steps in the Hallconductivity to lower magnetic fields. The Hall conductivity is neither enhanced nordiminished by the presence of this kind of defect alone. We also consider the presence oftwo defects on a sample, a screw dislocation together with a disclination. For a specificvalue of deficit angle, there is a reduction in the Hall conductivity. For an excess ofangle, the steps shift to higher magnetic fields and the Hall conductivity is enhanced.Our work could be tested only in common semiconductors but we think it opens a road to theinvestigation on how topological defects can influence other classes of Hall effect.