Combination mechanism of ionization and low-temperature conductivity

A combination electrothermal (ET) mechanism of ionization of neutral centers is demonstrated to exist. The corresponding ionization coefficient is calculated and conditions at which the ET mechanism becomes dominant in the process of ionization of neutral centers are elucidated. Investigations show that the ET ionization mechanism leads to an increase in the free-charge carrier density in the pre-breakdown state and for a low compensation factor reduces the breakdown electric field intensity, thereby leading to better agreement with the experimental data. I. Dzhavakhishvili Tbilisi State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–6, November, 1999.     

Frequency dependence of low-temperature phononless conductivity in disordered systems

The frequency dependence of resonant phononless hopping conductivity in disordered systems with pointlike centers of localization in the low-temperature limit is considered within the framework of the pair approximation. It is shown that the existing theory that predicts the power-mode frequency dependence of the low-frequency phononless hopping conductivity σ(ω) and a transition from linear to quadratic dependence (crossover) when frequency increases may become invalid, and the quadratic frequency dependence may never manifest itself at all.     

One-dimensional effects in low-temperature conductivity of ultrathin metallic filaments

The resistance of ultrathin filaments (UF) of Hg (with diameters 20–40 Å) increases as the temperature is lowered as $\text{ΔR/R ～ T}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}\text{(T < 60}\text{K}\text{)}$ and decreases with the applied electrical field as $\text{ΔR/R ～}\text{1}\text{E}$. The magnitude 1113 1104 of this effects increases as the diameter of UF is made smaller. Such temperature dependence is interpreted in terms of weak electron localization in one-dimension. The non-linearity of current-voltage characteristics of UF is due to electron-electron interactions in one-dimensional tunnel junctions.     

Characteristic features of the low-temperature thermal conductivity of highly-enriched and natural germanium

Experimental data on the thermal conductivity K(T) of natural and highly enriched (99.99%) Ge⁷⁰ crystals with ground and polished surfaces are analyzed in the temperature interval ∼2–8 K. In all samples, the boundary scattering mechanism predominates in the interval from 2 to 4.0 K. As temperature increases, in highly enriched samples N processes start to contribute to phonon transport and the behavior of K(T) corresponds to viscous Poiseuille flow of a phonon gas. The isotopic scattering mechanism plays a large role in isotopically nonideal samples. Fiz. Tverd. Tela (St. Petersburg) 40, 1604–1607 (September 1998)     

Single mode operation of the p-Ge FIR laser

The mode structure of p-Ge far infrared (FIR) lasers is investigated. Without external mirrors a multimode spectrum is observed. An external resonator drastically reduces the number of oscillating modes and enlarges the mode spacing. By changing the magnetic field a single line can be selected. By increasing the electric and magnetic field the single line can be tuned by steps of the mode spacing to shorter wavelengths.     

Non-ohmic conductivity of TaS3 in the low-temperature semiconducting regime

Electrical conductivity of the quasi one-dimensional conductor TaS₃ was measured in the low-temperature semiconducting regime. Below 100K, the conductivity along c-axis (l-d axis) in the low field limit is characterized by the activated process with the activation energy of 250K, and the current-field (I-E) characteristic is nonlinear, $\text{dI}\text{dE}$ increasing with the field strength. These results can be explained by the excitation of phase solitons associated with pinned CDW condensates.     

Relaxation of hot holes in p-Ge

Saturated absorption of infrared radiation by p-doped Ge is treated theoretically, predicting that both the saturation intensity and the width of the probe-saturator spectrum oscillate as functions of the saturator photon energy, ?ω. The maxima occur for ?ω = n?ω_LO, where n is an integer and ?ω_LO is the zone-center LO phonon energy. The results may a lso provide the closest measurement of hole cascade relaxation times to date. The oscillations depend on theoretical estimates that the LO phonon emissions occur substantially more rapidly than other decay processes. Hence failure to observe the oscillations would belie these estimates.     

Electrical conductivity in a layer formed by low-temperature grinding in germanium

Electrical-conductivity and Hall-effect measurements have been made for germanium surface layers damaged by grinding at room temperature and at low temperature (77 and 4.2 K). A comparison is made with cleaved surfaces. There are similarities and differences between the ground surfaces and those made by cleaving at low temperatures. The results are discussed on the assumption that most of the conductivity involves the microcrack walls.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 62–65, January, 1988.     

Effect of doping on the absorption spectra of p-Ge

Absorption spectra recorded at 295 and 94 ° K for p-Ge samples of various concentrations are reported. There is some discrepancy between these results and those reported previously. The absorption is calculated from the approximate Kahn theoretical equations, and the results are compared with experiment. The quantitative agreement is unsatisfactory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 68–72, June, 1970.     

Measurement of electrical conductivity of low-temperature alkali plasma by weak probing signals

A method for measuring the real component of the electrical conductivity in a plasma diode is described. The phase — sensitive detection enables to use extremely low probing signal down to 10 V.     

Spatial correlations of chaotic oscillations in the post-breakdown regime of p-Ge

Spatial correlations and long-range crosstalk of chaotic behaviour between two electrically separated parts of a single p-Ge crystal at 4.2 K are investigated and theoretically explained in terms of energy relaxation oscillations of two hot carrier subsystems, driven by impact ionization, and coupled by phonons.     

Pair tunneling in the low-temperature conductivity of the Cd-Sb alloy high-resistance state near the superconductor-insulator transition

We report a study of the temperature dependence, down to 30 mK, of the magnetoresistance of Cd-Sb alloy in the insulating phase obtained by annealing the quenched metallic superconducting ( _{T c} ≈4.5 K) phase of the alloy. Even though the sample in this state is no longer superconducting, the observed negative magnetoresistance points to single-particle tunneling in the presence of a superconducting gap in the spectrum. At magnetic fields B<T the ratio α(T,B)=R(T,B)/R(T,B=4 T)is found to be maximum at a temperature of about 0.1 K. This behavior indicates a change of the conductivity mechanism from single-particle tunneling to incoherent two-particle tunneling as the temperature decreases. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 713–718 (25 November 1996) Published in English in the original Russian Journal. Edited by Steve Torstveit.     

Determination of the impurity concentration in heavily doped inhomogeneous semiconductors from the measurement of the low-temperature conductivity

A method has been developed for determining the effective concentration of shallow impuritiesN ^* reponsible for the low-temperature conductivity in the vicinity of the metal-insulator transition for inhomogeneous samples of n-Ge:As. The method is based on the measurement of two ratios of sample resistance -R(4.2 K)/R(300 K), =R(2.0 K)/R(4.2 K) and the conductivity (4.2 K). The next step consists of plotting and (4.2) vs . Assuming that is the most reliable parameter, one can calculate, after an averaging procedare, the corrected values of ^*, ^*(4.2) and the resistivity at room temperature ^*(300)=[ ^{* *}(4.2)]^–1. Finally, using the known dependence (300)=f(N) for homogeneous samples, one can obtain the values ofN ^*. The dependences ofN ^* on and on are plotted. The scaling behavior of the conductivity of the Ge:As samples with corrected values of ^*(4.2) andN ^* has been observed down toT=100 mK.     

Zeeman splitting of excited boron states in p-Ge

The photothermal spectrum of shallow acceptors in p-Ge has been investigated at various magnetic field strengths up to 5.6 T at a temperature of 7.5 K by FIR-Fourier-spectroscopy. From the observed Zeeman splittings of the excited states of the boron acceptor the coefficients of the linear and quadratic field dependence have been evaluated andg-factors of theD-,C- and theG-transitions have been determined based on a standard group theoretical approach.     

Effect of γ irradiation on the low-temperature electrical conductivity and dielectric properties of TlGaSe2 crystals

Electrical conductivity and dielectric properties of single-crystal TlGaSe₂ have been studied as a function of γ irradiation dose in the 100–280 K range including the existence of an incommensurate phase. Anomalies in the form of maxima have been observed in the σ=f(T), tan δ=f(T), and ɛ=f(T) curves at the points of transition from the paraphase to incommensurate (IC) phase, T _i, and from the IC to commensurate phase, T _c. The increase in the quantities σ, tan δ, and ɛ observed initially with increasing irradiation dose is followed by their strong decrease and disappearance of the anomalies. It has been established that γ irradiation does not affect the phase transition temperatures T _i and T _c. Fiz. Tverd. Tela (St. Petersburg) 40, 1328–1331 (July 1998)     

Thermoelectromotive force of p-Ge with consideration for the phonon-drag effect

A series expansion over the anisotropy parameter was used to solve the Boltzmann kinetic equation and to study the temperature dependence of the differential thermoelectromotive force coefficient of p-Ge in the temperature range 20–80 K with consideration for the phonon-drag effect. The results of the calculations are consistent with the experimental data.Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 5–8, February, 1989.