RESONANT STRUCTURE IN THE CONDUCTIVITY OF 2-DIMENSIONAL HETEROJUNCTION SYSTEMS - A MEMORY FUNCTION-APPROACH

The resonant structure in the conductivity of a two-dimensional system such as a GaAs/ AlGaAs heterojunction is investigated using a memory function approach. In a one-subband model the memory function obtains the expected dependence of the plasmon resonance on the electron conce ntration. A nonanalytic behavior is, however, obtained when a two-subb and model is employed within the random phase approximation. In partic ular, a negative lifetime is found at low frequencies that is attribut ed to its inability to handle the full electron-electron interaction t enser. It is found that if certain matrix elements are discarded, the resulting memory function does become analytic. The result thus obtain ed for the electron lifetime agrees with experiment. In addition, the memory function calculated conductivity for the two-subband case shows a richer structure than the one-subband conductivity above.