Acoustic plasmons in a two-band metal

The properties of acoustic plasmon excitations and the conditions for their existence in a metal with two overlapping bands one of which is narrow (d-band) and the other broad (s-band) are discussed. Model calculations in which the d-electrons are treated in the tight-binding approximation and the s-electrons are assumed to be free are presented. The prospects for finding well defined acoustic plasmons in a real system are examined. The example of the V₃Ga crystal is considered in some detail.     

Microwave heating and evaporating of a large electron-hole drop in pure Ge

At the large microwave power level, we have observed a sharp increase of the m.w. absorption in magnetic field and an appearance of steps in the m.w. absorption kinetics. These steps are connected with the intense evaporation of drops caused by the m.w. field, which provides the existence of the dense cloud of free carriers surrounding the drop. The density of the cloud has been found to depend strongly on magnetic field.     

Internal circulation in a drop in an acoustic field

An investigation of the internal flow field for a drop at the antinode of a standing wave has been carried out. The main difference from the solid sphere case is the inclusion of the shear stress and velocity continuity conditions at the liquid-gas interface. To the leading order of calculation, the internal flow field was found to be quite weak. Also, this order being fully time dependent has a zero mean flow. At the next higher order, steady internal flows are predicted and, as in the case of a solid sphere, there is a recirculating layer consisting of closed streamlines near the surface. In the case of a liquid drop, however, the behavior of this recirculating Stokes layer is quite interesting. It is predicted that the layer ceases to have recirculation when [formula: see text], where [symbol: see text] is the liquid viscosity, mu is the exterior gas-phase viscosity, and M is the dimensionless frequency parameter for the gas phase, defined by M = i omega a2 rho/mu, with a being the drop radius. Thorough experimental confirmation of this interesting new development needs to be conducted. Although it seems to agree with many experiments with levitated drops where no recirculating layer has been clearly observed, a new set of experiments for specifically testing this interesting development need to be carried out.     

Disintegration of a drop in an external electrostatic field

Regular features of the disintegration of both a drop of a perfectly conducting liquid and a drop of a dielectric liquid into two or three parts in an external uniform electric field are studied using the principle of minimizing the potential energy of the final state of a closed system with spontaneous processes.     

Dispersing of a charged drop in an electrostatic field

The characteristics of the breakup of a charged drop in a uniform electrostatic field are calculated on the basis of Onsager’s principle of minimum dissipation of energy in nonequilibrium processes. The ranges of the physical parameters where daughter droplets are emitted from two tips and from one tip of an unstable parent drop and when emission is completely absent are found. The dimensionless radii, charges, and specific charges of the daughter droplets are determined. Zh. Tekh. Fiz. 69, 26–30 (December 1999)     

Capillary oscillations of a drop in an electric field

The capillary oscillations of a conducting spheroidal drop with small eccentricity in an electric field are studied. The effect of the electric field is to lower the natural frequencies of oscillations and the damping coefficient.     

Time delay in formation of a γ-phase electron-hole drop in germanium

An explanation is given for the long time delay in the formation of gamma phase EHD in germanium. The Cerenkov radiation of phonons by moving alpha drops at velocity mach 0.2–0.3 is calculated to be the controlling process in the time delay.     

Two-dimensional electron-hole system in a strong magnetic field

A theory of a 2-D e-h-system in a strong magnetic field is presented. Its properties drastically depend on the existence of the e-h-symmetry in it. In an asymmetric system excitons interact with each other and as a result can from magnetic biexcitons. The system is unstable to the formation of a charge-density waves (CDW) at low temperatures.     

Deep-impurity effects on dimensional resonance of a large electron-hole drop in germanium

Alfvén wave dimensional resonance of a large electron-hole drop is studied in detail in strained Ge doped with Zn impurities. Impurity scattering rate within the large drop is 2.7 × 10¹⁰ s⁻¹ for holes. This is larger than 1.2 × 10¹⁰ s⁻¹ for electrons. The difference causes an imbalance of microwave response between electrons and holes and enhances a helicon-like nature in magneto-plasma modes.     

Attachment of an electron-hole droplet to a donor

The attachment of an electron-hole droplet to a donor in Ge is considered using the density-functional method. We find the heat of solution of a donor in a droplet to be about 7 meV, and the electron density at the donor to be 32 times the carrier density in the droplet far from the donor. Effects on droplet pinning and recombination are discussed.     

Ordinary hall effect and spin-dependent phenomena in a two-band model ferromagnetic metal

The ordinary Hall constant of a compensated ferromagnetic metal is calculated so as to include spin-dependent scattering effects. Model calculations have been performed for two cases of Fermi surface topologies which could likely correspond to the case of iron. It is found that the Hall constant varies over a wide range, and in some cases changes sign as a function of the new scattering mechanism in a form similar to the one produced by magnetic break-down. Experiments, which in principle can distinguish between both physical situations, are suggested.     

Rapid formation kinetics of a long-lived electron-hole drop in Ge under pulsed excitation

The buildup of a large long-lived electron-hole drop in stressed Ge is studied using its Alfvén wave resonances. This microwave method permits rapid time resolution of the formation process after a short intense (100 nsec, 7 W) laser excitation pulse. A delay of about 1 μsec is observed before the drop radius rapidly increases from zero to ～ 100 μm within the next μsec. This is consistent with the interpretation that the photo-produced electron-hole pairs are quickly accelerated to the strain-induced potential minimum which is well within the crystal.     

Plasma in a metal layer exposed to an RF electric field

The response of electrons in a metal layer (sheet) to a variable electric field normal to the surface is studied under resonance conditions, i.e., when the frequency of the field is close to the plasma oscillation frequency. The electromagnetic field energy absorbed in the sheet is calculated.     

Instability of a charged spherical drop moving parallel to an external electrostatic field

It is shown that the pressure of electrostatic fields induced by the self-charge of a drop and by the polarization charge and aerodynamic pressure of a laminar gas flow around a moving charged drop acting simultaneously reduce the critical instability conditions for the surface of the drop. For these conditions, the spectrum of capillary oscillations of the drop is calculated. It is found that, at various values of the charge, field strength, and velocity of the drop, the vibrational instability of the drop surface develops through the interaction of different oscillation modes, namely, second and third, second and fourth, and third and fifth.     

Mean field solutions to singlet hopping and superconducting pairing within a two-band Hubbard model

The mean field Green function solution of the two-band singlet-hole Hubbard model for high-T _c superconductivity in cuprates (N.M. Plakida et al., Phys. Rev. B51, 16599 (1995), JETP 97, 331 (2003)) involves expressions of higher order correlation functions describing respectively the singlet hopping and the superconducting pairing. Rigorous derivation of their values is reported based on the finding that specific invariant classes of polynomial Green functions in terms of the Wannier overlap coefficients v _ij exist. The text was submitted by the authors in English.     

Nonlinear oscillations of a charged drop accelerated in an electrostatic field

An analytical asymptotic solution to the problem of nonlinear oscillations of a charged drop moving with acceleration through a vacuum in a uniform electrostatic field is found. The solution is based on a quadratic approximation in two small parameters: the eccentricity of the equilibrium spheroidal shape of the drop and the amplitude of the initial deformation of the equilibrium shape. In the calculations carried out in an inertial frame of reference with the origin at the center of mass of the drop, expansions in fractional powers of the small parameter are used. Corrections to the vibration frequencies are always negative and appear even in the second order of smallness. They depend on the stationary deformation of the drop in the electric field and nonlinearly reduce the surface charge critical for development of the drops’s instability. It is found that the evolutions of the shapes of nonlinearly vibrating unlike-charged drops differ slightly owing to inertial forces.