Regensburg 2010 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 50: Graphene and Carbon Nanotubes
HL 50.3: Talk
Thursday, March 25, 2010, 10:00–10:15, H15
Photon helicity driven electric currents in graphene — •J. Karch1, P. Olbrich1, M. Schmalzbauer1, Ch. Brinsteiner1, J. Eroms1, U. Wurstbauer1, M.M. Glazov2, S.A. Tarasenko2, E.L. Ivchenko2, D. Weiss1, and S.D. Ganichev1 — 1Terahertz Center, University of Regensburg, Regensburg, Germany — 2A.F. Ioffe Physico-Technical Institute, St. Petersburg, Russia
We report on the observation of photon helicity driven photocurrents in graphene. The currents are generated in single layer graphene by terahertz radiation from a cw molecular gas laser operating at a wavelength of 118mkm. The photocurrents are measured at normal incidence and reverse their signs upon reversing the radiation helicity. Besides a photon helicity dependent current we also observe a photocurrent in response to linearly polarized radiation. The microscopic mechanisms governing these effects are discussed. The in-plane photocurrents induced by normal incidence of radiation are forbidden by symmetry in an ideal infinite graphene structure. The appearance of such currents are an evidence for a symmetry reduction, for instance, caused by the shape asymmetry of the real finite-size sample, which results in the edge photogalvanic effect. The helicity-dependent and -independent signals demonstrate also a strong dependence on the light incidence angle, i.e. there are remarkable contributions to the photocurrent being odd in the incidence angle. These effects can be attributed to currents in the bulk of the sample and can be described by the circular photon drag effect stemming from the transfer of the photon momentum to the electron subsystem in graphene.