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

TL;DR

This paper investigates nuclear magnetic resonance and spin relaxation in AlAs quantum wells, revealing weak hyperfine interactions and electron-nuclear spin interactions affecting nuclear spin dynamics, with experimental and theoretical insights.

Contribution

It provides the first detailed experimental and theoretical analysis of NMR and spin relaxation in AlAs quantum wells, highlighting weak hyperfine coupling and electron-nuclear interactions.

Findings

Overhauser shifts are much smaller than in GaAs.

Nuclear spin-lattice relaxation depends on electron filling factor.

Resonant RF radiation reveals quadrupole splitting of $^{75}$As nuclei.

Abstract

The study of nuclear magnetic resonance and nuclear spin-lattice relaxation was conducted in an asymmetrically doped to $n\sim1.8\times10^{11}$ cm$^{-2}$ 16 nm AlAs quantum well grown in the $[001]$-direction. Dynamic polarization of nuclear spins due to the hyperfine interaction resulted in the so-called Overhauser shift of the 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 hyperfine interaction is weak. The nuclear spin-lattice relaxation time extracted from the decay of 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. 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 $^{75}$As nuclei was clearly resolved. Theoretical calculations performed describe well these experimental findings.