Dresden 2006 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 28: Transport in high magnetic field/Quantum Hall-effect
HL 28.2: Vortrag
Mittwoch, 29. März 2006, 16:45–17:00, HSZ 01
Surface-Acoustic-Wave study of the spin phase transition at ν=2/3 in narrow quantum wells — •Dimitri Dini1, Werner Dietsche1, Klaus von Klitzing1, Chris Mellor2, and Maik Hauser1 — 1Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany — 2School of Physics and Astronomy, Nottingham University, Nottingham, Great Britain
We measure the conductivity σxx at filling factor ν=2/3 using DC as well as surface acoustic wave (SAW) techniques. Surprisingly, we detect features related to the spin phase transition in DC measurement but not in SAW ones. Within the composite fermion picture, ν=2/3 corresponds to two fully occupied Landau levels (LLs). With increasing magnetic field a transition from unpolarized electrons (the two LLs have different spin polarization) to spin-polarized electrons (Zeeman energy so large, that only one spin-polarization dominates) is observed. At the transition point, where two LLs cross each other, the electronic system may consist of domains with different spin polarization. We present experimental results which show that the spin phase transition is visible in DC experiments caused by the disappearing of the gap at the crossing point between LLs, whereas the SAW-damping (which depends on the conductivity) with surface acoustic waves with frequencies from 100 MHz up to 1 GHz does not show any significant signal due to the phase transition. Even at large current, where we measure an increase of more than 300% in σxx with DC techniques due to the hyperfine interection with the nuclei, the σxx measured with SAWs shows no increase.