Dresden 2009 – wissenschaftliches Programm
HL 12.6: Vortrag
Dienstag, 24. März 2009, 11:00–11:15, BEY 81
Observation of the orbital circular photogalvanic effect in Si-MOSFETs — •J. Karch1, P. Olbrich1, C. Reitmaier1, D. Plohmann1, S. A. Tarasenko2, Z. D. Kvon3, and S. D. Ganichev1 — 1Terahertz Center, University of Regensburg, Regensburg, Germany — 2A. F. Ioffe Physico-Technical Institute, St. Petersburg, Russia — 3Institute of Semiconductor Physics, Novosibirsk, Russia
We report on the observation of the orbital circular photogalvanic effect (CPGE). The experiments are carried out on (001) oriented and miscut Si-MOSFETs. The fact of the existence of the CPGE in such structures is of particular importance. So far, the CPGE has only been detected in materials with strong spin-orbit coupling and described by microscopic mechanisms based on spin-related processes. In Si-MOSFETs the spin-orbit coupling is known to be vanishingly small, therefore, these mechanisms of the CPGE become ineffective. We demonstrated that in our structures in spite of the fact that the photocurrent is caused by transfer of the photon angular momentum to free carriers, it is not due to spin orientation but has a pure orbital origin. It results from the quantum interference of different pathways contributing to the free-carrier absorption of monochromatic radiation. For excitation we use terahertz radiation of a molecular optically pumped laser in the wavelength range between 77 and 280 μm. Depending on temperature and gate voltage, which varies the separation between size-quantized subbands, we induce Drude-like as well as direct intersubband transitions. We developed both microscopic and phenomenological theories well describing all observed features of the orbital CPGE.