Unusual anisotropy of inplane field magnetoresistance in ultra-high mobility SiGe/Si/SiGe quantum wells

We find an unusual anisotropy of the inplane field magnetoresistance with higher resistance in the parallel orientation of the field, B ∥ , and current, I, in ultra-high mobility SiGe/Si/SiGe quantum wells. The anisotropy depends on the orientation between the inplane field and the current relative to the crystallographic axes of the sample, and is a consequence of the ridges on the quantum well surface. For the parallel or perpendicular orientations between current and ridges, a method of converting the magnetoresistance measured at I ⊥ B ∥ into the one measured at I ∥ B ∥ is suggested and is shown to yield results that agree with the experiment.