Effects of Higher Landau Levels and Valley Degeneracy on Charge Density Wave Instability of Two-Dimensional Electrons in Strong Magnetic Fields

Abstract

A transition temperature to the charge density wave (CDW) state is calculated by the mean field approximation for a two-dimensional electrons in strong magnetic fields. Firstly the effect of the impurity potential is examined. The impurity scattering is treated by the self-consistent Born approximation. The critical strength of the impurity potential is obtained for the existence of the CDW state. Secondly it is shown that higher Landau levels affect the transition temperature only slightly. Thirdly the effect of valley degeneracy is considered for a two-valley system as in (100) Si MOS. The valley degeneracy is seen to be spontaneously lifted below a critical temperature T_v and the CDW transition occurs appreciably below T_v. The effect of screening of the Coulomb interaction is briefly discussed.