Theory of Native Orientational Pinning in Quantum Hall Nematics

The orientation of the electron-nematic states discovered in the quantum Hall regime of GaAs $[001]$ growth-direction quantum wells is pinned by a weak native source of anisotropy. In this Letter we explain that this property, which has remained mysterious over more than a decade of research, follows from the presence of both Rashba and Dresselhaus spin-orbit interactions. The hard transport direction of the nematic state is determined by the relative sign of the Rashba and Dresselhaus coefficients, and coincides with either the $[110]$ or the $[1\bar{1}0]$ crystallographic direction. Our theoretical estimate of the pinning energy is in agreement with experimental studies of the competition between native pinning and intentional pinning by an in-plane magnetic field.