Spin-Orbit Scattering and E-Field Effects in Disordered Metals Near the Metal-Insulator Transition

The results of two studies of disordered metals near their metal-insulator transition are presented: (i) A detailed comparison of Ge(,x)Au(,1-x) and B(,x)Cu(,1 -x) is carried out in zero magnetic field. GeAu, a high Z material, has been shown to exhibit strong spin-orbit effects in a magnetic field while BCu, a low Z material, has been shown to exhibit weak spin-orbit effects. Both materials have similar temperature dependent dc conductivity behavior in zero field and approximately linear mobility edges; (ii) A detailed study of the non-linear dc conductivity of GeAu and C(,x)Cu(,1-x) is carried out for 1.3K < T < 4.2K and for E-fields up to 500V/cm. Analyzing the (sigma)(E) data in the context of an electron gas heating model yields unphysically long electron relaxation times. Alternatively, the E-field can limit renormalization by raising the electron energy above the disordered potential. The system then changes from quantum mechanical scaling to classically diffusive behavior beyond a certain length scale. The temperature and E-field data can then give the characteristic lengths and prefactors for the transition.