Longitudinal magnetoresistance

Abstract

The longitudinal magnetoresistance is easier to analyse than the transverse magneto­resistance, and it is used here to study how the theoretically predicted behaviour depends on the details of the model chosen. It is found that for a multiply-connected Fermi surface like that of copper there is a large difference according as the scattering is through large or small angles, and that a very small amount of small angle scattering imposed on predomi­nantly isotropic scattering can have a powerful influence in increasing the difference between zero-field and high-field conductivity. The effects discussed arise from those orbits which pass through Brillouin zone boundaries and which in a high field greatly accelerate the relaxation process by connecting opposite sides of the Fermi surface. A detailed calculation is carried out for the longitudinal magnetoresistance of aluminium with the field along a cube axis, and it is found that except in very strong fields the observed behaviour is well accounted for by the nearly-free. electron model and a constant relaxation time.