Anisotropic state of two-dimensional electron gas in high Landau levels

When several Landau levels of a high mobility two-dimensional electron system are occupied, transport measurements reveal evidence for intriguing new phenomena at low temperature. Near half filling in the N=2 and higher spin-split Landau levels, dramatic resistance anisotropies are observed. Large magnetoresistance peaks form in one direction in the 2D plane while deep minima form in the in the orthogonal direction. Application of a parallel magnetic field can re-orient this anisotropy. Interestingly, in the N=1 Landau level, parallel fields not only suppress the energy gap of the ν=5/2 fractional quantum Hall state but also render the transport highly anisotropic