Coulomb Drag as a Probe of the Nature of Compressible States in a Magnetic Field

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Magneto-drag reveals the nature of compressible states and the underlying interplay of disorder and interactions. At ν=3/2 a clear T⁴/³ dependence is observed, which signifies the metallic nature of the N=0 Landau level. In contrast, drag in higher Landau levels reveals an additional contribution, which anomalously grows with decreasing T before turning to zero following a thermal activation law. The anomalous drag is discussed in terms of electron-hole asymmetry arising from disorder and localization, and the crossover to normal drag at high fields as due to screening of disorder.