Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 21: Spintronik III

HL 21.6: Talk

Saturday, March 5, 2005, 12:00–12:15, TU P164

All optical probe of dynamic nuclear spin polarization in n-GaAs — •Klaus Schmalbuch, Lars Schreiber, Marcus Heidkamp, Bernd Beschoten, and Gernot Güntherodt — II. Physikalisches Institut, RWTH Aachen, Templergraben 55, 52056 Aachen

Nuclear spins are a candidate for solid-state implementation of a quantum computer, since they are localized and exhibit spin relaxation times in the order of seconds. Electron spins can be used to address and control nuclear spins by the hyperfine interaction. Therefore we investigated dynamic nuclear polarization in bulk n-GaAs in small magnetic fields using all-optical NMR. Electron spins are coherently pumped by a circularly polarized laser pulse. Their orientation is probed by time-resolved Faraday rotation. The shift of their precession frequency (Overhauser shift) is a measure of the optically induced local nuclear field.

The strongest nuclear fields are observed after pumping localized electron spin states of the donor bands with time constants of the order of seconds. In contrast, delocalized electron spins with long spin lifetimes couple only weakly to the nuclear system. Those states can thus be used for fast read-out of the nuclear fields by the Overhauser shift using resonant spin amplification. Tilting the sample with respect to the laser beams further enhances the dynamic nuclear polarization. With this technique, we observe nuclear fields of several 10 mT at an external field of 10 mT.

  Supported by BMBF FKZ 01BM160