Screening and inplane magnetoresistance of anisotropic two-dimensional gas

In order to split the influence of the orbital and spin effects on the inplane magnetoresistance of a quasi two-dimensional (2D) gas we derive its linear response function and dielectric function for the case of anisotropic effective mass. This result is used for the calculation of elastic transport relaxation time of a quasi two dimensional system in a parallel magnetic field. The relaxation time is proved to be isotropic in the low density limit for the case of charged impurity scattering, allowing to separate the two contributions.