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 sam ples 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 previ ously reported [N. V. Agrinskaya, V. I. Kozub, and D. V. Shamshur, JET P 80, 1142 (1995)]. The results of an investigation of samples that ar e closer to the transition in the low-temperature region below 36 mK a re presented. It is discovered that the samples investigated (which do not exhibit the suppression of negative magnetoresistance at comparat ively high temperatures) display this effect at low temperatures and t hat, 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 temperatur es for the sample that is closest to the metal-insulator transition. T he results obtained are analyzed within existing theoretical models th at take into account the role of both the orbital and spin degrees of freedom. In particular, the low-temperature feature indicated is inter preted as a manifestation of positive magnetoresistance caused by spin effects. Nevertheless, it is shown within a detailed analysis supplem ented by numerical calculations that the observed suppression of the n egative magnetoresistance cannot be attributed only to the appearance of spin positive magnetoresistance. Moreover, the possibility of obser ving spin positive magnetoresistance is determined to a certain extent specifically by the suppression of the negative magnetoresistance com peting with it. (C) 1997 American Institute of Physics.