Experimental examination of anisotropic transport in the high Landau levels of the correlated 2D electron system

Anisotropie transport exists along orthogonal crystallographic directions in high quality (high mobility) 2D electron gases for magnetic fields producing Landau level filling factors greater than four. In this work we outline the results of sets of experiments that examine these findings following two potential etiologies of the anisotropic response: transport of high Landau level composite fermions through incidental density corrugations, or phase separation into different quantum Hall states within the high Landau levels forming striped phases. In support of the composite fermion picture, evidence is presented demonstrating the presence of composite fermion physics in Landau levels other than the lowest. In addition, sample surface properties are found that indicate a prevalent density corrugation in even ultra-high mobility samples. In support of the phase separation picture, current paths are deduced by varying contact configurations on the samples: these results indicate a distinct stripe direction that is orthogonal to the density corrugation suggested by the sample surface morphology but consistent with transport through systems with artificial ID density modulations. It is concluded that the anisotropic transport is due to phase separation of the 2D gas into stripes of alternating quantum Hall fluids with stripes oriented as displayed in the current path measurements.