NONLINEAR PHOTOMAGNETISM OF METALS - THEORY OF NONLINEAR PHOTOINDUCEDDC CURRENT

Photoinduced magnetic flux has recently been observed in normal metals exposed to light. This effect is partly due to the fact that the ligh t reflected from a metal surface transfers to the conduction electrons some of its quasimomentum. This creates a dc surface current which, f or an appropriate geometry, brings about the photomagnetic effect. The re is another contribution to the current that is due to anisotropy of the probabilities of electron transitions induced by the light, in co mbination with diffuse reflection of the electrons at the surface. We present here a theory of the dependence of the photoinduced current on the intensity of light Q. We assume that the light intensity is eithe r constant or the time scale of its variation is much larger than the inverse Rabi frequency corresponding to the interband electron transit ion. At comparatively low intensities the current is proportional to Q . At higher intensities it varies as Q(1/2). The physical origin of su ch behavior is analyzed. Various factors that allow a lowering of the critical intensity for the onset of the nonlinear behavior are discuss ed.