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Thursday, September 18th 2014

1:25 pm:

In this talk, I will revisit a few old issues in the quantum Hall effect in high quality two-dimensional electron systems (2DES). I will first present our experimental results to quantitatively examine the theoretical model of spin splitting collapse in the quantum Hall regime [by Fogler and Shklovskii, Phys. Rev. B 52, 17366 (1995)] at fixed magnetic fields as a function of electron density in a high quality heterojunction insulated-gate field effect transistor. In the second part, I will talk about the quantum criticality of quantum Hall (QH) plateau to plateau transitions in alloy disordered two-dimensional electron systems. In one short-range random alloy disorder dominated sample, a perfect temperature (T) scaling, (dRxy/dB)|Bc T-, was observed through two full decades of T from 1.2K down to 12 mK. This manifests unequivocally that in an Anderson disordered 2DES the scaling behavior indeed prevails. Moreover, our temperature and size dependent data allow direct determination of both the localization critical exponent, = 2.38, and the dynamical exponent, z = 1. If time permits, I will also talk about the resistivity law observed ~ 30 years ago. Our recent work in ultra-high mobility 2DES has brought new insight on this problem.

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