ν=2/3 fractional quantum Hall state in an AlAs quantum well probed by electron spin resonance

Abstract

The electron spin resonance (ESR) of two-dimensional electrons confined in a high-quality, 16-nm AlAs quantum well was investigated near the filling factor $\ensuremath{\nu}=2/3$ of the fractional quantum Hall effect (FQHE). The spin resonance was robust in the vicinity of the fractional filling $\ensuremath{\nu}=2/3$, indicating that the $\ensuremath{\nu}=2/3$ state is at least partially spin polarized. The formation of the $2/3$ FQHE state did not result in any modifications of the ESR linewidth and, hence, of the electron spin relaxation rate. Yet the nuclear spin-lattice relaxation rate extracted from the time decay of the ESR Overhauser shift demonstrated a strong nonmonotonic dependence on the electron filling factor with a minimum near $\ensuremath{\nu}=2/3$. This observation suggests the enhancement of the energy gap in the spin excitation spectrum of two-dimensional electrons at the $\ensuremath{\nu}=2/3$ state.