Magnetoresistance anisotropy in Si/SiGe in tilted magnetic fields: Experimental evidence for a stripe-phase formation

We observe pronounced transport anisotropies in magnetotransport experiment s performed in the two-dimensional electron system of a Si/SiGe heterostruc ture. They occur when an in-plane field is used to tune two Landau levels w ith opposite spin to energetic coincidence. The observed anisotropies disap pear drastically for temperatures above I K. We propose that our experiment al findings may be caused by the formation of a unidirectional stripe phase oriented perpendicular to the in-plane field.