Magnetoresistance in semiconductor structures with hopping conductivity: Effects of random potential and generalization for the case of acceptor states

Abstract

We reconsider the theory of magnetoresistance in hopping semiconductors. First, we have shown that the random potential of the background impurities affects significantly preexponential factor of the tunneling amplitude which becomes to be a short-range one in contrast to the long-range one for purely Coulomb hopping centers. This factor to some extent suppresses the negative interference magnetoresistance and can lead to its decrease with temperature decrease which is in agreement with earlier experimental observations. We have also extended the theoretical models of positive spin magnetoresistance, in particular, related to a presence of doubly occupied states (corresponding to the upper Hubbard band) to the case of acceptor states in 2D structures. We have shown that this mechanism can dominate over classical wave-shrinkage magnetoresistance at low temperatures. Our results are in semi-quantitative agreement with experimental data.

Interference mechanism of magnetoresistance in variable-range hopping conduction: The effect of paramagnetic electron spins and continuous spectrum of scatterer energies

“…While semiconductors with hopping conductivity usually exhibit a combination of negative linear and positive quadratic magnetoresistance (this fact is in accordance with conventional magnetoresistance theory), the temperature dependence of negative and positive magnetoresistance differs sometimes from predicted by existing theories [13][14][15][16][17][18][19]. In [13,15,19] this difference is attributed to spin effects. In [15,19] the spin alignment magnetoresistance (suggested in [5]) is invoked to describe experimental observations.…”

“…In [13,15,19] this difference is attributed to spin effects. In [15,19] the spin alignment magnetoresistance (suggested in [5]) is invoked to describe experimental observations. However no rigorous theory of this magnetoresistance (and any consistent discussion of free spins effect on the magnetoresistance)is presented.…”

Interference mechanism of magnetoresistance in variable range hopping: the effect of paramagnetic electron spins

“…Let us compare our results with experimental data observed in [10,11]. This experiments show the unusual magnetoresistance dependence on temperature, namely, the suppression of negative magnetoresistance at low temperatures.…”

“…This experiments show the unusual magnetoresistance dependence on temperature, namely, the suppression of negative magnetoresistance at low temperatures. The spin mechanisms of magnetoresistance was suggested to understand this phenomena in [11], however no detailed theory of this mechanisms was given.…”

“…We also note that the existing theory of interference contribution to magnetoresistance is not sufficient to describe existing experimental data. For example there were observations of the suppression of negative magnetoresistance [10,11] at low temperature that can not be described with conventional theory.…”