Quantum versus semiclassical analysis of the conductivity of two-dimensional electrons in a magnetic field

Hayne, M and Usher, Alan and Harris, Jeffery J and Foxon, C Tom (1997) Quantum versus semiclassical analysis of the conductivity of two-dimensional electrons in a magnetic field. Physical Review B, 56 (16). pp. 10446-10452. ISSN 1550-235X

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Abstract

We present experimental evidence for the levitation of extended slates of a two-dimensional electron system in a magnetic field, and establish the presence of alternating regions of localized and extended states in the density of states to Landau-level filling factors (nu) as high as 80. Monitoring the Hall voltage of a modulation-doped GaAs/AlxGa1-xAs heterojunction at fixed magnetic field during continuous illumination from light-emitting diodes reveals a steplike structure with plateaus at even integer nu between 22 and 80 at a temperature of 0.3 K. We derive a general expression for the conductivity due to rectangular bands of extended states, and show that the observed temperature dependence of the Shubnikov-de Haas oscillations is consistent with this picture. An analysis of the oscillations using this expression reveals the predicted levitation of the extended states.

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