Anisotropic scattering of conduction electrons on point defects in Al

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Abstract
New Hall effect experiments on Al containing Zn, Mg or Ge impurities are discussed and compared with previous experiments on Al containing Frenkel defects; interstitials and vacancies. The low field Hall coefficient is found to change always in the positive direction, with respect to its strong negative isotropic value, this effect being largest for Ge doped Al and Frenkel defect Al, where even a positive sign for Hall coefficient is obtained. Kohler rule investigations show that anisotropic scattering of electrons on point defects is the origin of this effect. The relaxation time anisotropies are explained as originating from corresponding strong differences of the wavefunctions involved. This is proved by OPW charge density calculation for k states on the realistic Fermi surface of Al. The symmetrized results, as contour plots, show strong, expected differences. A simple qualitative measure of anisotropy is derived for both impurity and Frenkel scattering.