Negative magnetoresistance in the variable-range-hopping regime inn-type GaAs

Abstract

Low-field magnetoresistance measurements for compensated, n-type three-dimensional GaAs with net donor concentration just below the metal-insulator transition show a quadratic field dependence for values of 8 less than 750 G. Temperature-dependent measurements in zero 6eldshow that transport is by variable-range hopping, and are consistent with the presence of a Coulomb gap which narrows close to the transition. It is found that the temperature dependence of the eff'ective area in which the Aux is enclosed is not related to the temperature dependence of

NEGATIVE MAGNETORESISTANCE BEHAVIOURS AND LOCALIZED MAGNETIC MOMENTS IN INSULATING CdSe SEMICONDUCTOR AT VERY LOW TEMPERATURES WITH MAGNETIC FIELD

“…We observed that the curve obtained can be adjusted by a straight line that gives us the following law: ). This behaviour is similar to those obtained by Trembey [18] and Capoen [31] on GaAs samples, Zhang and Sarachik [19] on CdSe samples. These authors found that ) ( 1 T f has the same variation with temperature, regardless of the impurities concentration of samples and of the regime of conduction observed.…”

“…We observed that in the limit of low fields, the NMR varies linearly with 2 B and the slopes ) ( 1 T f of these straight lines decrease when the temperature increases. We also noticed that the value of magnetic field m B , from which the linearity deviation occurs increases with temperature, which is good agreement with the theory proposed by Entin-Wohlman [18]. The NMR has been adjusted using the following form:…”

“…Quadratic NMR with magnetic field has been observed experimentally in the VRH regime in a number of insulating materials [18][19][20][21][22]. Schirmacher [23] have had proposed another analysis of NMR in presence of VRH regime using the following expression:…”

Hopping conduction in uniaxially stressed Si:B near the insulator-metal transition

“…This was attributed [10,12] to hopping energies that were larger than the gap energy at high temperature (Mott hopping) and smaller than the gap at low T (ES hopping). A crossover with dopant concentration was found in n-GaAs [13], where Mott hopping was claimed for samples near the metal-insulator transition when the Coulomb gap has a small energy-width, and ES hopping prevails deeper in the insulating phase where electron-electron interactions are stronger and the hopping electrons probe the gap. Although variable-range hopping exponents have been found that deviate from these values, it is found that strong electron interactions yield a hopping exponent of 1/2 while weak interactions (compared with hopping energies) give rise to exponent 1/4.…”

“…Although variable-range hopping exponents have been found that deviate from these values, it is found that strong electron interactions yield a hopping exponent of 1/2 while weak interactions (compared with hopping energies) give rise to exponent 1/4. This has given rise to the expectation that Mott variable-range hopping will always be observed near the metal-insulator transition as electron screening increases and the Coulomb gap collapses approaching the metallic phase [13,14].…”