Experimental studies of the higher Landau levels in the 2D electron system

Abstract

The high Landau levels have demonstrated numerous interesting phenomena with theoretical models in need of specific experimental support. While the composite fermion picture provides a model for the series of correlated electron liquids states manifesting as the fractional quantum Hall effect in the lowest Landau level, this model finds its limits in the higher Landau levels. Here transport phenomena such as anisotropic conductance at the half-filled levels dominate the magnetoresistance spectra, which is ostensibly due to phase separation into stripes of integral filling. In the B-field range between these anisotropy findings in the high Landau levels and the FQHE of the lowest Landau level, the anomalous state at 5 2 filling factor has presented an enigmatic variation on the standard liquid states normally found exclusively at odd-denominator filling. This unique state has been suggested to result from composite fermion pairing in d or p wave. In this work we show results independently addressing these theoretical models for the striped phase and the 5 2 state. We show magnetoresistance data that specifically indicates striped phase formation in the 2DES, also depicting the direction of the stripes within the sample. At smaller filling factors in surface acoustic wave measurements we show evidence for the composite fermion model of pairing to form the 5 2 state by demonstrating Fermi surface formation at temperatures above those at which the 5 2 is quantized in Hall resistance.