Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 26: III-V semiconductors I

HL 26.7: Vortrag

Dienstag, 26. Februar 2008, 17:15–17:30, EW 202

Observation of dynamic nuclear polarization in GaAs(001) quantum wells close to a GaMnAs layer — •R. Schulz, A. Wagner, T. Korn, U. Wurstbauer, D. Schuh, W. Wegscheider, and C. Schüller — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, 93040 Regensburg, Germany

GaMnAs is a highly interesting material system for future spintronic devices, where both, spin and charge of carriers are manipulated. Here, we present a study of nonmagnetic GaAs quantum wells (QW) embedded in AlGaAs barriers close to a ferromagnetic GaMnAs layer. The samples contain two QWs, where one QW (12nm width) is close to the GaMnAs layer, separated by a thin AlGaAs layer and a short-period superlattice AlAs/GaAs. The second QW (10 nm width) is farther away (120 nm) and serves as a reference.
Time-resolved Faraday rotation experiments reveal a significantly increased spin lifetime in the upper QW (12 nm) of about 3 ns compared to the lower QW (10 nm) of about 130 ps. This long spin lifetime causes a dynamic nuclear polarization via the hyperfine interaction and thus an effective magnetic field. By tilting the sample with respect to the pump beam, this effective magnetic field has an in-plane component, which may add to or subtract from an external in-plane magnetic field, changing the Larmor precession frequency of the electron spins depending on the sign of the magnetic field, the intensity and helicity of the circularly-polarized pump beam.
We acknowledge support by the DFG via project SCHU1171/1 and SFB 689 TP B4.