Interplay of Disorder and Coulomb Interactions in Anderson-Localized States

Abstract

This paper discusses a general theoretical treatment to investigate the rival effects of disorder and electron-electron interactions in the Anderson-localized regime. First it is shown that the intrastate interaction gives rise to the occurrence of singly occupied states as well as doubly occupied states near and below the Fermi level and that this results in a Curie-type spin susceptibility at low temperatures. Secondly it is shown that electron-electron interactions between Anderson-localized states lead to both ferromagnetic (direct exchange) and antiferromagnetic (kinetic-type exchange) interactions among spins of singly occupied states. Specific heat anomaly beyond the T-linear behavior, in particular its magnetic field dependence, and magnetic susceptibility at very low temperatures are calculated by taking into account the coexistence of ferromagnetic and antiferromagnetic interactions within a spin pair model. It is shown that the experimental results on Si:P can be well explained by the present treatment. Finally the effects of electron-electron interactions on the magnetoresistance of the variable range hopping conduction are investigated. It is shown that magnetoresistance is positive as far as the change of localization length due to a magnetic field is neglected. Taking into account the latter effect which is responsible for negative magnetoresistance, the total magnetoresistance including positive and negative parts is calculated for the system of lT-TaS₂ which is considered to be two dimensional. The peculiar features of magnetoresistance observed in that system can be explained well by the present theory.