Reorientation of the anisotropic phase of a 2D electron system using a very small density modulation

A high-quality two-dimensional electron system (2DES) confined to a GaAs quantum well typically exhibits isotropic transport coefficients when the Fermi level resides in the first excited ($N=1$) Landau level. Adding an in-plane magnetic field ($B_{||}$) leads to an anisotropic (stripe) phase with the stripes oriented perpendicular to the $B_{||}$ direction. We study how a periodic density modulation of the 2DES, induced by a surface strain grating from lines of negative electron-beam resist, affects the orientation of the $\nu=7/2$ stripe phase. Our results reveal that the external potential modulation competes against the $B_{||}$-induced orientational order of the stripe phase. Even a minute ($\sim0.5\%$) density modulation is sufficient to reorient the stripes at $\nu=7/2$ along the direction of the surface grating.