Electron scattering and transport phenomena in small-gap zinc-blende semiconductors

We give expressions for electrical conductivity, thermoelectric power and thermal conductivity of conduction band electrons in small-gap zinc-blende semiconductors, obtained by solving the Boltzmann equation by a variational procedure. The term resulting from the phonon-drag is included in the Boltzmann equation. The following electron scattering mechanisms are investigated: inter and intraband scattering by optical phonons via polar and nonpolar interactions, scattering by charged centers (ionized defects and heavy holes) and by neutral centers, as well as scattering by acoustic phonons. Particular attention is paid to the screening of the electron-optical phonon polar interaction by free carriers, which is particularly important in the case of a linear energy band. The formula for the intraband RPA dielectric function for the case of the linear band is given.The general formulation of all the problems investigated permits direct application of the results given in this paper to both intrinsic or n-type HgTe-type and InSb-type semiconductors, including mixed crystals, e.g. Cd_xHg_1?xSe near the cross point.     

Electron capture in the collision of a proton with a hydrogen atom

Electron capture in the collision of a proton with a hydrogen atom is investigated. The probability of electron capture is calculated from first principles by the direct solving of the three-dimensional nonstationary Schr?dinger equation. The dependence of the probability of electron capture by a proton on the proton??s velocity and impact parameter is obtained and analyzed thanks to highly efficient computations with the use of graphic processing units.     

Disordered solids: Universal behavior of structure, dynamics, and transport phenomena

Disordered materials (glasses and amorphous substances, melts, polymers, biological media, etc.) are an important class of objects. Despite the chaos usually associated with their structure, glasses and amorphous substances of various kinds (semiconducting, dielectric, metallic) possess a universal spatial scale length ∼1 nm, an order parameter, which can be as important theoretically as the unit cell for crystals. The disorder in disordered substances is not absolute; the periodicity positions of atomic inherent in crystals is maintained within a few coordination spheres and is then somehow destroyed. The way in which the order breaks down makes it possible to distinguish the glasses from amorphous materials in terms of the form of the structural correlation function. The inhomogeneities in question are not exotic, unique formations or analogs of defects in crystals, but are the fragments out of which amorphous substances and glasses are entirely constructed. The spatial inhomogeneity of disordered substances having a characteristic scale length of ∼1 nm leads to some universal characteristics in their vibrational properties, changes the relaxation mechanism for electronic excitation, and determines the specific features of charge transport. Fiz. Tverd. Tela (St. Petersburg) 41, 805–808 (May 1999)     

Excitation of the hydrogen subsystem in metals and alloys by ionizing radiation

Models of nonequilibrium-stimulated diffusion and the release of hydrogen and its isotopes from metals by the action of ionizing radiation are considered. It is suggested that the acceleration of the release of hydrogen from metals by the action of radiation is due to the excitation of nonequilibrium vibrational states in the hydrogen subsystem of the metals and a reduction in the surface potential barrier by the desorbing molecules. It is shown, in particular, that the diffusion coefficient of deuterium in Pd is increased by a factor of 30 by the action of radiation compared with a nonirradiated sample. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–10, November, 1998.     

Excitation of the hydrogen subsystem in metals and alloys by ionizing radiation

The results of research on the nonequilibrium liberation of deuterium from niobium, palladium, and stainless steel under electron-beam bombardment are reported. The maximum on the deuterium gas liberation curve in the low-temperature region is shown to shift under linear heating with simultaneous electron-beam bombardment in comparison with linear heating without such bombardment. The shift reaches 130° in Nb, 100° in stainless steel, and 65° in Pd. The rate of radiation-stimulated gas liberation increases nonlinearly with the concentration of deuterium introduced and the electron-beam current. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, p. 41–46. July, 1998.     

High-density phenomena in hydrogen plasma

A novel path-integral representation of the many-particle density operator is presented which makes direct Fermionic path-integral Monte Carlo simulations feasible over a wide range of parameters. The method is applied to compute the pressure, energy, and pair distribution functions of a hydrogen plasma in the region of strong coupling and strong degeneracy. Our numerical results allow one to analyze the atom and molecule formation and breakup and predict, at high density, proton ordering and pairing of electrons.     

Electron proton instability in the CSNS ring

The electron proton (e-p) instability has been observed in many proton accelerators. It will induce transverse beam size blow-up, cause beam loss and restrict the machine performance. Much research work has been done on the causes, dynamics and cures of this instability. A simulation code is developed to study the e-p instability in the ring of the China Spallation Neutron Source (CSNS).     

Electron proton instability in the CSNS ring

The electron proton (e-p) instability has been observed in many proton accelerators. It will induce transverse beam size blow-up, cause beam loss and restrict the machine performance. Much research work has been done on the causes, dynamics and cures of this instability. A simulation code is developed to study the e-p instability in the ring of the China Spallation Neutron Source (CSNS).     

On the description of transport phenomena

The linear response of a quantity like the electric current to a time and space dependent field can be described by Kubo's formula, and this again can be written as a resolvent. The expansion of this resolvent yields exactly a transport equation of the structure of the Boltzmann equation. Perturbation theory — the only practical way to deal with it — gives back the usual Boltzmann equation. This derivation has advantages like yielding a symmetric collision operator. Also including time and space dependence with this approach is very easy. The purpose of this paper is to show the closeness of linear response theory and kinetic equations. We also discuss merits and drawbacks of the resolvent method.     

Gravitational anomaly and transport phenomena

Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.     

Reconstruction of bands in metallic hydrogen

The generalized theory of normal properties of a metal for the case of the properties of the electronic band of electron–phonon systems with a variable electron density of states is used to study the normal phase of metallic hydrogen at a pressure of 500 GPa and a temperature of 200 K. We calculated the frequency dependence of the real ReΣ(ω) and imaginary ImΣ(ω) parts of the self-energy part of the electron Green’s function Σ(ω), as well as the electron density of states N(ε) of the stable phase of metallic hydrogen with the I41/amd symmetry at a pressure of 500 GPa, renormalized by the strong electron–phonon coupling. It is found that the electron conduction band of the I41/amd phase of metallic hydrogen undergoes insignificant reconstruction near the Fermi level because of the renormalization by the electron–phonon coupling.     

Collisional phenomena and current buildup in the electricalbreakdown of hydrogen

The electrical breakdown of hydrogen is examined by means of a two-dimensional mathematical model applied to the case of a 0.50-mm gap at atmospheric pressure. The calculations indicate a very rapid discharge development, characterized by a marked deviation of the axial density profiles from an exponential dependence, but with an approximately exponential variation of the discharge current. The axial-electron and ion-density profiles are similar in form and nearly balanced in magnitude. Notwithstanding the small magnitude of the space-charge field, the radial profiles of the electron and ion density displayed a definite tendency towards constriction, i.e., the incipient formation of a spark-type channel     

Electronic and magnetic states in metallic compound—II: Electron transport and magnetic susceptibility in NiAl and FeAl

Electron transport and magnetic properties were investigated in NiAl and FeAl alloys in the vicinity of exact stoichiometry. The results as well as those of other workers were compared with recent augmented-plane-wave band calculations for NiAl, and semiquantitative agreement was found. With respect to impurity states in NiAl, it was concluded that transport anomalies, though definitely magnetic in origin, were not due to localized-magnetic moments on excess Ni atoms on Al sites. It was suggested that the anomalies may be due to subtle structural defects or such defects in combination with one of several intrinsic (non-impurity or defect) mechanisms. In the FeAl alloys, it was concluded that excess Fe atoms on Al sites (Fe_x atoms) carry a moment in the paramagnetic state of 7·8 μ_B. Negative magneto-resistance but no resistance minima effects were observed. The data, similar in several respects to those for dilute Rh(Fe) alloys, were interpreted in terms of antiferromagnetically coupled Fe_x atoms which lead to magnetic transitions of a spin-glass or mictomagnetic nature, that is, having no long-range order.     

Linear dynamics of a magnetic subsystem in a quasi-Ising magnet

Microwave absorption at frequencies from 37 to 85 GHz was studied for a Dy_0.3Y_2.7Fe₅O₁₂ single crystal in pulsed magnetic fields of up to 30 T at T=4.2 K. The magnetic field was aligned with the [100] direction. For the fields above 4 T, several soft magnetic-resonance modes were observed, most of them being caused by the static phase transitions induced by a strong external magnetic field. The field-independent absorption lines away from the points of phase transition may be due to the dynamic Jahn-Teller magnetic effect.     

High-frequency dynamics in metallic glasses

Using inelastic x-ray scattering we studied the collective dynamics of the glassy alloy Ni33Zr67 in the first pseudo-Brillouin-zone, an energy-momentum region still unexplored in metallic glasses. We determine key properties such as the momentum transfer dependence of the sound velocity and of the acoustic damping, discussing the results in the general context of recently proposed pictures for acoustic dynamics in glasses. Specifically, we demonstrate the existence in this strong glass of well defined (in the Ioffe-Regel sense) acoustic-like excitations well above the boson peak energy.