Orbital and spin effects in the low-temperature behavior of the magnetoresistance of doped CdTe crystals

An observation of the suppression of negative magnetoresistance in samples of doped CdTe that are far from the metal-insulator transition as the temperature is lowered in the temperature range 3–0.4 K was previously reported [N. V. Agrinskaya, V. I. Kozub, and D. V. Shamshur, JETP 80, 1142 (1995)]. The results of an investigation of samples that are closer to the transition in the low-temperature region below 36 mK are presented. It is discovered that the samples investigated (which do not exhibit the suppression of negative magnetoresistance at comparatively high temperatures) display this effect at low temperatures and that, as previously, the suppression of the negative magnetoresistance correlates with the transition to conduction via Coulomb-gap states. A plateau-like magnetoresistance feature is displayed at low temperatures for the sample that is closest to the metal-insulator transition. The results obtained are analyzed within existing theoretical models that take into account the role of both the orbital and spin degrees of freedom. In particular, the low-temperature feature indicated is interpreted as a manifestation of positive magnetoresistance caused by spin effects. Nevertheless, it is shown within a detailed analysis supplemented by numerical calculations that the observed suppression of the negative magnetoresistance cannot be attributed only to the appearance of spin positive magnetoresistance. Moreover, the possibility of observing spin positive magnetoresistance is determined to a certain extent specifically by the suppression of the negative magnetoresistance competing with it. Zh. éksp. Teor. Fiz. 111, 1477–1493 (April 1997)