Regensburg 2010 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 37: Quantum Dots and Wires: Optical Properties III
HL 37.10: Talk
Wednesday, March 24, 2010, 12:00–12:15, H15
Exciton mediated dynamic nuclear polarzation in an individual self-assembled quantum dot — Florian Klotz, Vase Jovanov, •Johannes Kierig, Emily C. Clark, Daniel Rudolph, Dominik Heiss, Max Bichler, Gerhard Abstreiter, Martin S. Brandt, and Jonathan J. Finley — Walter Schottky Institut, Am Coulombwall 3, 85748 Garching, Germany
We present investigations of dynamic nuclear polarization (DNP) in a single self-assembled InGaAs/GaAs quantum dot subject to an external magnetic field (B0) and electric field parallel to B0. Resonant excitation of the neutral exciton (X0) is shown to lead to a buildup of nuclear spin orientation due to tunneling escape of photoexcited carriers that serves to recycle dark states formed by hyperfine-mediated electron-nuclear spin flip-flop processes. DNP was achieved by tuning one Zeeman level of X0 into resonance with a single frequency laser to optically pump spin-polarized carriers. We estimated the resulting Overhauser field BN by locating both Zeeman branches relative to a measurement where DNP was inhibited. The saturation value of BN depends on whether sweeps are performed from low to high electric fields or vice versa, B0 and the timescale over which the sweeps are performed. BN is always found to be oriented parallel to B0 with magnitude BN∼3−5 T. In addition, we also performed time resolved measurements of the nuclear spin orientation dynamics and found BN to increase over timescales ranging from a few seconds to several minutes depending on the excitation intensity, electric field and detuning from resonance.