NEGATIVE MAGNETORESISTANCE IN THE VARIABLE-RANGE-HOPPING REGIME IN N-TYPE CDSE

The magnetoresistance in the variable-range-hopping regime of compensated, n-type CdSe measured between 1.6 and 6 K in the Ohmic regime at small magnetic fields is negative and obeys the expression DELTA-R/R = f (T)B2, with f(T) approximately T-a and a = 1.32 +/- 0.04. As in recent experiments by Tremblay et al. on GaAs, this temperature dependence is observed for all samples independently of whether the resistivity at zero field indicates Mott hopping or variable-range hopping in the presence of a Coulomb gap. This implies either that the relevant dephasing time is not the hopping time, or that our current understanding of the negative magnetoresistance in these materials is incomplete.