Dresden 2009 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 23: Transport in high magnetic field/quantum-Hall-effect
HL 23.2: Talk
Tuesday, March 24, 2009, 14:15–14:30, BEY 154
FQHE measurements on a GaAs/GaAlAs high mobility sample — •Lina Bockhorn1, Annelene F. Dethlefsen2, Frank Hohls1, Werner Wegscheider3, and Rolf J. Haug1 — 1Institut für Festkörperphysik, Leibniz Universität Hannover — 2Centre for Atom Optics and Ultrafast Spectroscopy, Faculty of Engineering and Industrial Science, Swinburne University of Technology — 3Institut für Experimentelle und Angewandte Physik, Universität Regensburg
We study the fractional Quantum-Hall effect in high mobility two-dimensional electron systems (2DES). Hall geometries are created by photolithography on a GaAs/GaAlAs heterostructure containing a 2DES. The mobility and the density of electrons are manipulated by illuminating the samples with a LED and by using a topgate. For a given density of electrons we study the Shubnikov-de Haas-oscillations for different temperatures to extract the activation energies.
We observe a Hall plateau at filling factor 5/2 for a mobility of electrons with 4· 106 cm2/Vs. We can detect the Hall plateau at 5/2 for temperatures up to 270mK. For several other filling factors we observe an astonishing linear magnetic dependence of the activation energy for small magnetic fields and a cross-over to square root dependence for high magnetic fields.