Magnon instability by a radiation field in magnetic semiconductors and strong d.c. magnetic fields

The magnon damping in an electron-magnon system in the presence of a laser beam and a d.c. magnetic field is discussed. It is shown that near the laser-cyclotron resonance, and for the laser beam propagating perpendicularly to the magnetic field the magnon population in a relatively narrow range of k may grow with time.     

On the d.c. conductivity in semi-insulating GaAs

We investigate the temperature dependence of electrical conductivity of SI-GaAs. We have shown that the surface conductivity obeys the Berthelot type of dependence, the bulk component, on the other hand, fulfills the Arrhenius dependence.     

PAC-study of defects in n-type germanium

Using perturbed angular correlations of γ rays the behaviour of Frenkel defects in n-type germanium is studied.¹¹¹In/¹¹¹Cd probes either serve as primary knock-on atoms in the production of Frenkel defects by neutrino recoil or as trapping agents for defects produced by electron irradiation. The neutrino recoil process leads to a defect which is characterized by vQ=e²qQ/h=42(2) MHz (η=0.6), while a defect with vQ=423(1) MHz (η=0) is observed after electron irradiation and thermal annealing.     

Hopping conductivity of Ni-doped p-CdSb in strong magnetic fields

Magnetoresistance (MR) of oriented single crystals of the anisotropic semiconductor p-CdSb doped with 2 at% of Ni is investigated between T=1.5 and 300 K in transversal pulsed magnetic fields up to B=30 T. In fields B∼4-15 T at T below 4.2 K, the resistivity obeys the law ln ρ∼η[B?(B)]^1/2 with ?(B)=a(0)/a(B), where a is the carrier localization radius and parameter η depends on a(0), on the acceptor concentration N_A and on the direction of the magnetic field with respect to the crystallographic axes, but does not depend on T. Such behavior gives evidence for MR realized by hopping charge transfer over the nearest-neighbor sites in strong magnetic field. The analysis of the experimental data yields the values of η, agreeing with calculated ones within an error of 10%, taking into account the effects of the anisotropy of the acceptor states and of the explicit dependence of a(B) due to the increase in the activation energy of shallow acceptors in magnetic field and the sensitivity of the metal-insulator transition to B.     

Palladium-vacancy pairs in p-type and n-type germanium

Time differential perturbed angular correlation spectroscopy was performed for n-type and p-type germanium samples that had been recoil-implanted with the probe ¹⁰⁰Pd/¹⁰⁰Rh. Two different measurements with the detectors aligned along <100> and <110> crystallographic directions of germanium confirm that the palladium probe pairs with the nearest neighbour vacancy and not a dopant. The pairs interact with a coupling constant of υ _Q = 10.7(2) MHz and this agrees with what has been observed in undoped Ge. This further suggests that the palladium pairs with a vacancy in germanium, doped or un-doped. It was also observed that there are more Pd-V pairs in Ga-doped than there are in Sb-doped Ge. DFT calculations of the binding energies of the Pd-defect complexes support the experimental observations.     

The complex conductivity of the plasma of a d. c. sustained arc discharge

An expression is sought for the complex conductivity of the, plasma of an arc discharge sustained by a strong direct current for the case that a very weak high-frequency current passes through the plasma without influencing it in any way. The agreement between the results obtained and existing conceptions is satisfactory.     

Anomalous behavior of the electrical conductivity tensor in strong magnetic fields

The behavior of the electrical conductivity tensor in strong magnetic fields in the presence of unclosed quasiclassical electron trajectories of complex form near the Fermi surface is considered. It is shown that the asymptotic behavior of the conductivity tensor in the limit B→∞ differs in this case from the picture previously described for trajectories of simpler form. The possibility of blocking the longitudinal conductivity in strong magnetic fields at low temperatures in the case of a Fermi surface of special form is also treated theoretically. Zh. éksp. Teor. Fiz. 112, 1710–1726 (November 1997)     

Phonon-assisted d.c. hopping conductivity at a weak electron-phonon coupling

For a model of electrons in a complete set of localized states interacting with harmonic phonons, an exact asymptotic formula for the d.c. phonon-assisted hopping conductivity at low values of the electron-phonon coupling constant is derived. This formula agrees formally with a classical result of Kasuya and Koide, contradicting thus the present understanding of the hopping transport. Reasons of this disagreement as well as a correspondence with the experiment are discussed.     

Electric conduction in n-type germanium and cadmium sulfide

The impurity conduction of n-type Ge and CdS is calculated via a previously developed theory for impurity bands in doped semiconductors. Rough agreement with experimental data over a wide range of impurity concentration is found. The comparison with AMO-MT calculation shows a large enhancement due to a stronger electron correlation.     

DC electrical conductivity of vanadium-borate glass in weak and strong electric fields

The results of an investigation of the temperature and field dependences of the electrical conductivity of vanadium-borate glass with the composition 32.56% V₂O₅, 46.18% B₂O₃, and 21.26% CaO (mole %) are discussed. The measurements were carried out on metal-glass-metal sandwich structures in the temperature interval 200–500°K with electric field intensities up to 10⁸ V/m. It is shown that the experimental data for T 350°K can be described within the framework of the percolation conductivity theory with a variable jump length, which permits explaining the value of the critical field and the temperature dependence of the slope of the current-voltage characteristics (CVC). It is proposed that for T > 350°K the essential role in forming the CVC is played by small-radius polarons (SMP) localized in the vicinity of positively charged defect centers (bound SRP).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 90–94, May, 1982.     

Charge carrier transport and d.c. conductivity in thin polycrystalline p-terphenyl films2

The electrical conductivity and charge carrier mobility in thin polycrystalline p-terphenyl layers have been measured. The transport and conductivity were interpreted in terms of a hopping mechanism. The activation energies of mobility and conductivity were obtained, and the density of states in the vicinity of the Fermi level 10²⁰ cm^?3 eV^?1 was estimated. The height of the potential barrier around the impurity levels changed according to the Poole-Frenkel effect.     

Electrical conductivity characteristics of soda-lime-silicate glasses in strong electrical fields after gamma irradiation

Stable radiation-induced changes of electrical conductivity in strong electric fields in soda-lime-silicate glasses is explained using the concept that the accumulation of volume charge creates a high-voltage polarization in the presence of electrons excited by gamma irradiation. It is assumed that the processes of recombination of electrons and sodium cations, and their dissociations, are controlled by the strong electric field.     

Rotational Brownian dynamics simulations of non-interacting magnetized ellipsoidal particles in d.c. and a.c. magnetic fields

The rotational Brownian motion of magnetized tri-axial ellipsoidal particles (orthotropic particles) suspended in a Newtonian fluid, in the dilute suspension limit, under applied d.c. and a.c. magnetic fields was studied using rotational Brownian dynamics simulations. The algorithm describing the change in the suspension magnetization was obtained from the stochastic angular momentum equation using the fluctuation-dissipation theorem and a quaternion formulation of orientation space. Simulation results are in agreement with the Langevin function for equilibrium magnetization and with single-exponential relaxation from equilibrium at small fields using Perrin's effective relaxation time. Dynamic susceptibilities for ellipsoidal particles of different aspect ratios were obtained from the response to oscillating magnetic fields of different frequencies and described by Debye's model for the complex susceptibility using Perrin's effective relaxation time. Simulations at high equilibrium and probe fields indicate that Perrin's effective relaxation time continues to describe relaxation from equilibrium and response to oscillating fields even beyond the small field limit.     

Impurity dependence of the low temperature annealing in n-type germanium

Lightly doped n-type Ge, irradiated at liquid He temperatures with 1 MeV electrons, exhibits a large thermal recovery stage at 50–70°K. We have found that the rate at which this stage anneals depends on the type of group V impurity used to dope the sample. We Propose that impurity complexes are involved in this annealing stage. We have also observed the same impurity dependence when this annealing stage is destroyed by radiation annealing at liquid He temperatures. This suggests that one of the defects produced during irradiation is free to migrate at very low temperatures.     

Dispersion of the nonlinear optical susceptibility of n-type germanium

We observe a strong impurity-induced resonance in the third-order nonlinear optical susceptibility of n-type germanium. Our observations are used to obtain the cross-sections for electronic Raman scattering between the valley-orbit split 1s states of phosphorus and arsenic donors near 10 μm. Good agreement is found between measurements and calculations. The possibility of obtaining tunable impurity Raman laser action in n-type germanium is discussed.     

The temperature dependence of the electrical conductivity in amorphous germanium

An investigation of the electrical conductivity in amorphous Ge has been made. It has been found that the temperature dependence of the conductivity can differ from the usually acceptedT ^–1/4 law. It has been shown that transition from the hopping-type conductivity can be influenced by the conductivity in extended states.Cukrovarnická 10, Praha 6, Czechoslovakia.We are grateful to dr. B. Velický for discussions about the subject matter of this paper and to Mr. J. Zemek for preparation of germanium samples.     

Breakdown of a gas in superimposed d.c. and h.f. electric fields

By means of a time resolution it was found that the electric breakdown of air at atmospheric pressure between a charged plate and a spike, on which a torch discharge is burning, gaves rise to comparatively stable ellipsoidal plasma formations — plasmoids. Their dimensions stay within 2÷10 mm, velocity 0÷4 ms, acceleration –210÷1500 ms^–2. Their life time is 10^–2 s in magnitude. They decay either at the spike electrode, or when the actual breakdown takes place, or they desintegrate in the inter-electrode space.     

The kinetics of the annealing of irradiation damage at low temperatures in n-type germanium

The annealing which occurs always near 65K following low-temperature electron-irradiation of n-type germanium is governed by second order (or higher) annealing kinetics. It follows that the experimental activation energy must vary from experiments performed on high resistivity material where the defect concentration is low to those on low resistivity material where the defect concentration is high. A model for the annealing of defects which accounts for this observation and involves the diffusion of ionized interstitials, is suggested.