Regensburg 2002 – scientific programme

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HL: Halbleiterphysik

HL 13: Hauptvortrag

HL 13.1: Invited Talk

Tuesday, March 12, 2002, 10:15–11:00, H15

Monitoring electron-nuclear spin interactions with a fractional quantum Hall ferromagnet — •J. Smet — Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, 70569 Stuttgart

Correlations frequently force the two-dimensional electron system to order in a genuine ferromagnetic ground state, not unlike those of familiar low dimensional ferromagnets. For example, when two composit fermion Landau levels with opposite spin quantum numbers and different cyclotron energies simultaneously approach the chemical potential, the exchange energy cost for spin misalignment induces a ferromagnetic phase transition with easy axis unisotropy. This density driven transition is accompanied by hysteresis and domain formation. Time-dependent transport and resistively detected NMR studies assign a prominent role to the contact hyperfine interaction between the electron system and the nuclear spins of the host semiconductor for the dynamics of domains. We will show that the sensitivity of this ferromagnetic ground state on the degree of nuclear spin polarization can be exploited as a spectroscopy tool to detect gapless or low-energy collective modes in the electronic system. The developed procedures can even be combined to carry out the control transver of spin angular momentum between electrons and the nuclei of the host semiconductor using gate voltages only.