Kinetic equation for a weakly interacting classical electron gas

A kinetic equation is derived for the two-time phase space correlation function in a dilute classical electron gas in equilibrium. The derivation is based on a density expansion of the correlation function and the resummation of the most divergent terms in each order in the density. It is formally analogous to the ring summation used in the kinetic theory of neutral fluids. The kinetic equation obtained is consistent to first order in the plasma parameter and is the generalization of the linearized Balescu-Guersey-Lenard operator to describe spatially inhomogeneous equilibrium fluctuations. The importance of consistently treating static correlations when deriving a kinetic equation for an electron gas is stressed. A systematic derivation as described here is needed for a further generalization to a kinetic equation that includes mode-coupling effects. This will be presented in a future paper.     

On the origin of two-dimensional electron gas states at the surface of topological insulators

The ab initio calculations of the electronic structure in the bulk and at the (0001) surface of narrow-band Bi₂Se₃, Sb₂Te₃, Sb₂STe₃, and Sb₂SeTe₂ semiconductors have been performed. It has been shown that ternary compounds Sb₂STe₂ and Sb₂SeTe₂, as well as the previously known compounds Bi₂Se₃ and Sb₂Te₃, are three-dimensional topological insulators. The influence of the subsurface van der Waals gap expansion on the surface electronic structure of these compounds has been analyzed. It has been shown that this expansion leads to the formation of new (trivial) surface states, namely a parabolic state in the conduction band and an M-shaped state in the valence band. These results explain the phenomena discovered recently in photoemission experiments and reveal the nature of new states that are caused by the adsorption of atoms on the surfaces of the layered topological insulators.     

Driven quasi-one-dimensional classical electron gas in the presence of a constriction: Pinning and depinning

We studied the properties of a quasi-one-dimensional system of charged particles in the presence of a local Lorentzian-shaped constriction. We investigated the response of the system when a time-independent external driving force is applied in the unconfined direction. Langevin molecular dynamics simulations for different values of the drive and temperature are performed. We found that the particles are pinned unless a threshold value of the driving force is reached. We investigated in detail the depinning phenomenon. The system can depin “elastically”, with particles moving together and keeping their neighbors, or “quasi-elastically”, with particles moving together through a complex net of conducting channels without keeping their neighbors. In the case of elastic depinning the velocity vs applied drive curves is characterized by a critical exponent β consistent with the value , while in the case of quasi-elastic depinning the critical exponent β has on average the value 0.94. The model is relevant e.g. for electrons on liquid helium, colloids and dusty plasma.     

Phase transitions in condensed media at a finite rate of formation of a metastable state

The influence of the finite rate of formation of a metastable state on the kinetics of the first-order phase transition is analyzed. The conditions determined by the thermodynamic parameters and the cooling rate of the system under consideration are derived. Under these conditions, the formation of the metastable state can be treated either as an instantaneous process, when nucleation occurs at the end of the cooling stage, or as a slow process, when intensive nucleation of a new phase proceeds within the cooling stage. An equation describing the time and temperature that correspond to intensive nucleation of new-phase particles is obtained. The nucleation stage of the new phase takes place in the immediate vicinity of the temperature determined from this equation. All the other parameters, which determine the kinetics of the initial and transient stages of the phase transition, are calculated with respect to this temperature. As an example, all the relationships for a weak solid solution are presented.     

Subband structure of a two-dimensional electron gas formed at the polar surface of the strong spin-orbit perovskite KTaO3

We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, our measurements provide a direct upper bound for the potential Rashba spin splitting of only Δk(parallel)}~0.02 ?(-1) at the Fermi level. The polar nature of the KTaO3(100) surface appears to help mediate the formation of the 2DEG as compared to nonpolar SrTiO3(100).     

Cluster structure of condensed media

This paper presents the results of a theoretical study of cluster formation in condensed media for simple and multi-atomic liquids, as an example. A two-parameter function is proposed by the authors for the density of the probability distribution of clusters, which corresponds to a disordered condensed media, depending on the number of constituent particles. Using this function, the universal mean, most probable, and rms numbers of particles in clusters of noble gases, liquid metals, and some organic liquids were calculated. As well, the cluster component of total entropy for the substances under study was computed.     

Photogalvanic current in electron gas over a liquid helium surface

We study the stationary surface photocurrent in 2D electron gas near the helium surface. Electron gas is assumed to be attracted to the helium surface due to the image attracting force and an external stationary electric field. The alternating electric field has both vertical and in-plane components. The photogalvanic effect originates from the periodic transitions of electrons between quantum subbands in the vertical direction caused by a normal component of the alternating electric field accompanied by synchronous in-plane acceleration/deceleration due to the electric field in-plane component. The effect needs vertical asymmetry of the system. The problem is considered taking into account a friction caused by the electron-ripplon interaction. The photocurrent resonantly depends on the field frequency. The resonance occurs at field frequencies close to the distance between well subbands. The resonance is symmetric or antisymmetric depending on the kind (linear or circular) of polarization.     

Realization of a spin-polarized two-dimensional electron gas via image-potential-induced surface states

Electrons in image-potential-induced surface states form a two-dimensional electron gas in front of the surfaces. In the case of ferromagnets, their binding energies as well as lifetimes depend on the orientation of their spin magnetic moment with respect to the magnetization direction. Various experiments with inverse photoemission and two-photon photoemission to detect the spin dependence of image states are reviewed. A new and successful approach to achieve and detect a spin-polarized two-dimensional electron gas is presented, namely polarization-dependent and spin-resolved two-photon photoemission. Additional time resolution opens the way to study spin-dependent electron dynamics.     

Microscopic theory of some surface effects in a dense electron gas

We consider interacting electrons confined to a slab of finite thickness or a half space in the random phase approximation. The electronic charge is assumed to be neutralized by a homogeneous positive background. A linear response function is introduced from which it is possible to calculate the induced density variation of the electron gas, caused by an external field. The linear response function also determines the Helm-holtz free energy and, by a sum rule, the density of the undisturbed system. The interaction of a classical point charge with the electrons of a half-space is discussed. In addition, a formula for the surface energy is given.     

Exchange energy density of inhomogeneous electron gas near a metal surface

Using the first-order density matrix of an infinite barrier model of a metal surface, the exchange energy density can be evaluated exactly as a function of the distance z from the barrier. This result is compared with the local approximation $\text{?}\text{3}\text{4}\text{e}{}^2\text{(}\text{3}\text{π}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{[?(z)]}{}^{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}$ where the electron density in the model. The local approximation follows the exact result quite closely at all z but leads to a large percentual error in the integrated surface exchange energy.     

Theory of a condensed charged-bose,charged-fermi gas

Field-theoretic methods are used to derive the low-temperature properties of a dense, neutral gas of condensed charged (+Ze) bosons (mass M) and degenerate charged (?e) fermions (mass m). The density-density correlation function exhibits two collective modes for m ? M: a plasmon branch and a phonon branch with speed $\text{c = V}{}_{\mathrm{F}}\text{(}\text{Zm}\text{3M}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. Boson single-particle excitations are gapless and coincide with the phonon mode at low k. Inclusion of the two interacting dynamical components leads to small shifts in the boson and fermion ground-state energy and boson depletion relative to the values obtained for models with rigid, inert, neutralizing backgrounds.     

Equation of state of condensed media

A new choice is proposed for the generating functional which is used to obtain an integral equation for the radial distribution function that is valid in the domain of dense fluids. The corresponding equation of state for giving the intramolecular potential in the form (r)r ^–s agrees in the case of dense fluids with the known Tait empirical equation of state. The Tait equation is extended to the high-pressure case. Processing the experimental data for water exhibits good agreement between the equation of state obtained and experiment in the pressure range from 10⁵–10⁹ Pa.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 43–47, December, 1981.     

Internal structure of a classical spinning electron

A classical model of the spinning electron in general relativity consisting of a rotating charge distribution with Poincaré stresses is set up. It is made out of a continuous superposition of thin charged shells with differential rotation. Each elementary shell is maintained in stationary equilibrium in the gravitational field created by the others. A class of interior solutions of the Kerr-Newman field is thus obtained. The corresponding stress-energy tensor naturally splits into the sum of two terms. The first one is the Maxwell tensor associated to a rotating charge distribution, and the second one corresponds to a material source having zero energy density everywhere, no radial pressure, and an isotropic transverse stress. These negative pressures or tensions are identified with the cohesive forces introduced by Poincaré to stabilize the Lorentz electron model. They are shown to be the source of a negative gravitational mass density and thereby of the violation of the energy conditions inside the electron.     

Initial state dependence of nonlinear kinetic equations: The classical electron gas

The method of nonequilibrium cluster expansion is used to stydy the decay to equilibrium of a weakly coupled inhomogeneous electron gas prepared in a local equilibrium state at the initial time,t=0. A nonlinear kinetic equation describing the long time behavior of the one-particle distribution function is obtained. For consistency, initial correlations have to be taken into account. The resulting kinetic equation-differs from that obtained when the initial state of the system is assumed to be factorized in a product of one-particle functions. The question of to what extent correlations in the initial state play an essential role in determining the form of the kinetic equation at long times is discussed. To that end, the present calculations are compared with results obtained before for hard sphere gases and in general gases with strong short-range forces. A partial answer is proposed and some open questions are indicated.