CHAOTIC EFFECTS IN ELECTRON DRAG PROCESSES IN METALS

We investigate theoretically and experimentally the dependence of the electron drag force on the magnetic field H in normal metals. The conv entional theory assumes a linear increase with increasing H. Here we d emonstrate that F(H) proportional to H-beta. Our experiments with a zi nc crystal give beta = 2.27. Theoretically, assuming diffusive motion, we obtain 2 1/3 < beta < 2 1/2. Unlike the linear theory where the cy clotron motion remains unaffected by the dislocation potential, here w e show with numerical simulations that an isolated dislocation gives r ise to chaotic scattering. The origin of the nonlinear dependence of t he drag force is related to the substantial deviation of a typical ele ctron trajectory from its unperturbed cyclotron motion. Using a topolo gical criterion of chaos, the diffusion coefficient was estimated as D proportional to 1/\K\(1/2), where K is the Gaussian curvature of the potential energy surface. The diffusive motion is seen to result from the combined effects of deterministic chaotic motion (by a single disl ocation) and the scattering by randomly distributed defects in a real sample.