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It is shown that the linear resistivity dependence on temperature for metals above the Debye’s temperature mainly is caused by electron-electron scattering of randomly moving electrons. The electron mean free path in metals at this temperature range is in inverse proportion to the effective density of randomly moving electrons, i.e. it is in inverse proportion both to the temperature, and to the density-of-states at the Fermi surface. The general relationships for estimation of the average diffusion coefficient, the average velocity, mean free length and average relaxation time of randomly moving electrons at the Fermi surface at temperatures above the Debye’s temperature are presented. The effective electron scattering cross-sections for different metals also are estimated. The calculation results of resistivity dependence on temperature in the range of temperature from 1 K to 900 K for Au, Cu, Mo, and Al also are presented and compared with the experimental data. Additionally in temperature range from 1 K to 900 K for copper, the temperature dependences of the mean free path, average diffusion coefficient, average drift mobility, average Hall mobility, average relaxation time of randomly moving electrons, and their resultant phonon mediated scattering cross-section are presented.

The distribution of the static magnetic field around a superconducting torus is obtained. The superconductor is assumed to be an ideal diamagnet. Under this assumption an analytical expression for the magnetic field distribution around a torus is derived for the first time. This also takes into account magnetic flux trapping. The current density distribution on the torus surface and the magnetic field distribution around the superconducting torus were calculated for three cases: (1) when the torus is cooled down far below the critical temperature T c in zero external magnetic field and then the external magnetic field is switched on; (2) when the torus is cooled down in non-zero external field; (3) when the torus was cooled down as in the previous case and then the external field was switched off. All these cases are illustrated by diagrams. The magnetic flux quantization effect is deduced from classical electrodynamics and gauge symmetry.

High-frequency relative intensity noise, mode-suppression ratio and cross-spectra of low-frequency optical and electrical noise were measured in 1.55 /spl mu/m strained-layer multi-quantum-well (MQW) InGaAsP/InP laser diodes, which underwent accelerated aging. The deterioration of the linewidth and side-mode-suppression ratio is accompanied by an increase in the negative correlation between the optical noise and terminal electrical noise in the vicinity of the threshold. This is explained by recombination processes through point defects in some areas of the active layer, which contributes to an intensive Lorentzian noise. An absence of both the Lorentzian noise and negative correlation between optical and electrical fluctuations at threshold indicate higher quality laser operation. It is, therefore, concluded that measurements of the correlation factor could be used as convenient method in laser quality screening.

Low-frequency noise characteristics and their changes during short-time ageing of InGaAsP multiquantum-well distributed-feedback laser diodes were measured with the aim of investigating the reliability of devices. The noise characteristics reveal obvious differences between the stable and degrading lasers operated near the threshold region - an excessive Lorentzian type noise with negative correlation factor was observed at the threshold of degrading devices. The behaviour of the degrading lasers during ageing could be explained by migration of point recombination centres at the interface of an active layer, and by the formation of defect clusters.

Some studies on the magnetic flux trapped in a hollow superconductor and an applicability of the hollow superconductor for magnetic shielding are reported.

The optical and electrical low-frequency noise spectra and their correlation factor of multiple quantum well strained-layer Fabry-Perot (F-P) and distributed-feedback (DFB) InGaAsP/InP laser diodes have been investigated as a function of temperature and current. Particular attention has been given to the optical and electrical fluctuations due to mode-hopping effects, which are observed in the F-P lasers at specific currents and temperatures. Both the electrical and optical noise during mode hopping have a Lorentzian type spectrum, and are very strongly correlated and very sensitive to temperature and optical feedback.

The low‐frequency noise characteristics in Bi‐based superconductor thick films have been measured as a function of frequency, temperature, bias current, and applied magnetic field. These results have been compared with the resistance, temperature coefficient of the resistance dependences on temperature, and also with ones of Y‐based thick film superconductor. Our investigation shows that the peak of the voltage noise is not related with the peaks both of the temperature coefficient of the resistance and the voltage‐to‐flux transfer function. We suppose that voltage fluctuations are taking place at grain boundaries (weak Josephson links) between superconducting and normal grains, and that depend on the relative filling of the film by the superconducting grains. We represent a model that explains the resistance fluctuation peak in the superconducting transition temperature region.

1 ƒ noise dependence on temperature for both n- and p-type silicon has been measured. The formula for calculation of 1 ƒ noise is presented. The formula has been derived by presumption that only lattice scattering gives 1 ƒ noise. A good agreement between calculations and experimental results is found.

We report measurements of low frequency 1/f excess noise for the series of La0.75Sr0.25MnO3 (LSMO) giant magnetoresistive thin epitaxial films with thickness of 42, 50, 100, and 600 Å. Fabricated manganite films experience semiconductor-normal metal (paramagnetic-ferromagnetic) phase transition with the temperature change. The transition manifests itself by the sharp change of resistivity and characteristic peak of magnetoresistivity. Thickness decrease results in lowering the transition temperature and increasing of resistivity. The noise spectra has 1/fa behavior with a ≈ 1± 0.2. The voltage fluctuations spectral density shows quadratic dependence on current indicating that observed noise is caused by the resistance fluctuations. Noise level, temperature coefficient of resisistvity and magnetoresistance increase for thin films. Therefore, the operation point (transition temperature) can be tailored from 330 K to 220 K by changing only the film thickness while the performance of temperature and magnetic field LSMO sensors can be maintained almost constant in thickness range down to 100 Å.

International audience

International audience

International audience