Last update: 07.02.2005    

    Magneto-Gyrotropic Photogalvanic Effects
in Semiconductor Quantum Wells.

V.V. Bel'kov*,**, S.D. Ganichev*, E.L. Ivchenko**, S.A. Tarasenko**, W. Weber*, S. Giglberger*,
M. Olteanu*, H.-P. Tranitz*, S.N. Danilov*, Petra Schneider*, W. Wegscheider*, D. Weiss*, and W. Prettl*

* Fakult¨at Physik, University of Regensburg, 93040, Regensburg, Germany and
** A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia

(Dated: January 31, 2005)


Recently spin photocurrents generated in QWs and bulk materials have attracted considerable attention. Experimentally, a natural way to generate spin photocurrents is the optical excitation with circularly polarized radiation. However, in an external magnetic field spin photocurrents may be generated even by unpolarized radiation. In this paper we show that free-carrier (Drude) absorption of both linearly polarized and unpolarized terahertz radiation in quantum well (QW) structures causes a spin polarized electric photocurrent in the presence of an in-plane magnetic field. The results agree with the phenomenological description based on the symmetry. Experimental and theoretical analysis evidences that the observed photocurrents are spin-dependent and related to the gyrotropy of the QWs. Microscopic models for the photogalvanic effects in QWs based on asymmetry of photoexcitation and relaxation processes are proposed showing that there are a variety of new routes to generate spin polarized currents. As we used both magnetic fields and gyrotropic mechanisms we coined the notation ''magneto-gyrotropic photogalvanic effects'' for this class of phenomena. In addition, our results show that, without a magnetic field, non-equilibrium free carrier heating can be accompanied by spin flow. (PDF)