Münster 1999 – scientific programme
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HL: Halbleiterphysik
HL 39: Symposium: Quanten Hall Systeme
HL 39.5: Fachvortrag
Friday, March 26, 1999, 11:30–12:00, H1
Huge longitudinal resistance at fractional filling factors — •W. Dietsche1, S. Kronm üller1, K. v.Klitzing1, G. Denninger2, and W. Wegscheider3 — 1Max-Planck-Institut für Festkörperforschung — 2Universit ät Stuttgart — 3Walter Schottky Institut, TU München, 85748 Garching,Deutschland
One signature of the fractional quantum Hall effect state is the vanishing o f the longitudinal resistance at fractional fillings of a Landau level. In quantum well samples where the thickness of the well is reduced to about 15 nm instead of the more common 25 nm one finds rather huge resistance maxima at certain fractional fillings. This unusual behavior occurs only if the measurements are made on a time scale of several minutes and with a sufficiently large current. It is suspected that this novel phenomenon is related to a dynamical polarisation of the Ga and the As nuclei in the well which is caused by the current flow. The main evidence comes from the observation of a resistively detected NMR in this system: irradiation with radio frequencies corresponding to the splitting of the nuclear magnetic moments leads to substantial decreases in the resistance. Even more striking is the splitting of the NMR lines into four sub lines which seems to be in contradiction with the degeneracies of the I=3/2 nuclei. A qualitative description of the data uses a hyperfine enhanced coupling between neighbouring nuclear dipoles. Such a model, however, requires the existence of a novel correlated state between the electrons and the nuclear magnetic moments.