Highly anisotropic transport in the integer quantum Hall effect

At very large tilt of the magnetic (B) field with respect to the plane of a two-dimensional electron system the transport in the integer quantum Hall regime at nu =4, 6, and 8 becomes strongly anisotropic when two electrical subbands are occupied. At these filling factors the usual deep minima in the magnetoresistance occur for the current flowing perpendicular to the in-plane B field direction but develop into strong maxima for the current flowing parallel to the in-plane B field. The origin of this anisotropy is unknown but resembles the recently observed anisotropy at half-filled Landau levels.