Breaking of Larmor's theorem in quantum Hall states with spin-orbit coupling

We investigate the effect of spin-orbit (SO) interaction on the long-wavelength collective spin excitation in a two-dimensional electron gas in the fractional quantum Hall regime. The many-body correction to the single-particle electron spin resonance (ESR) energy is found to be nonzero, providing theoretical evidence of a breaking of Larmor's theorem. Such breaking is due to the loss of spin-rotational invariance introduced by the SO-induced structural inversion asymmetry in the system. This effect, whose magnitude is a significant percentage of the single-particle ESR, exhibits remarkable features in a wide range of experimentally relevant parameters and is found to be nearly material independent.