Higher Landau Levels

Abstract

The integer quantum Hall effect is observed even in such a low magnetic field that more than ten Landau levels are occupied. On the other hand, the fractional quantum Hall effect ceases to be observed in higher Landau levels. In the higher Landau levels, new types of ground states are realized, and the ordinary fractional quantum Hall states are replaced by such states. Concretely, in the second lowest Landau level, apart from the ordinary fractional quantum Hall effect at v =7/3 and 8/3, a similar effect at v = 5/2 is observed. In the third and higher Landau levels, the fractional quantum Hall effect has never been observed. Instead, a strongly anisotropic diagonal resistivity is observed at low temperature, and this is regarded as being due to the formation of a unidirectional CDW, or stripe state. In this chapter the experimental results and physics underlying these phenomena are explained.