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HL: Fachverband Halbleiterphysik

HL 71: Quantum Dots: Optical Properties

HL 71.8: Vortrag

Donnerstag, 17. März 2011, 12:15–12:30, POT 251

Asymmetric optical nuclear spin pumping in a single uncharged quantum dot — •Florian Klotz¹, Vase Jovanov¹, Johannes Kierig¹, Emily Clark¹, Max Bichler¹, Gerhard Abstreiter¹, Heike Schwager², Geza Giedke², Martin Brandt¹, and Jonathan Finley¹ — ¹Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748 Garching — ²Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching

We present the observation of a unipolar optically pumped dynamic nuclear polarization (DNP) in a single self assembled InGaAs quantum dot (QD). Electrons are resonantly excited in the QD and polarize the nuclear spin system via the hyperfine contact coupling, creating an Overhauser magnetic field. Remarkably, we observe a strong asymmetry in nuclear spin pumping for excitation of the two Zeeman-split neutral exciton states. Hereby, pumping the higher energy Zeeman branch effectively polarizes the nuclear spin system, whereas the lower energy branch does not. We also find a characteristic dependence of the observed DNP on the applied magnetic field where optically induced nuclear spin pumping is most efficient for an intermediate regime of 4 - 6 T, with a polarization of the nuclear spin bath of 53%. A theoretical model is developed that successfully explains the empirically found features based on the exciton level structure of the system.