Nuclear magnetic resonance and nuclear spin relaxation in AlAs quantum well probed by ESR

The study of nuclear magnetic resonance and nuclear spin-lattice relaxation was conducted in an asymmetrically doped to n~1.8×10¹¹0.28em0excm^-216 nm AlAs quantum well grown in the $[001]$ direction. The dynamic polarization of nuclear spins due to a hyperfine interaction resulted in the so-called Overhauser shift of two-dimensional conduction electron spin resonance. The maximum shifts achieved in the experiments are several orders of magnitude smaller than in GaAs-based heterostructures, indicating that the hyperfine interaction is weak. The nuclear spin-lattice relaxation time extracted from the decay of the Overhauser shift over time turned out to depend on the filling factor of the two-dimensional electron system. This observation indicates that nuclear spin-lattice relaxation is mostly due to the interaction between electron and nuclear spins. The Overhauser shift diminishes resonantly when the rf radiation of certain frequencies was applied to the sample. This effect served as an indirect, yet powerful, method for nuclear magnetic resonance detection: NMR quadrupole splitting of ⁷⁵As nuclei was clearly resolved. Theoretical calculations performed describe well these experimental findings.