Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by Optically Pumped NMR

TL;DR

This study investigates ultra-slow electron spin dynamics in GaAs quantum wells near the fractional quantum Hall state nu=1/3 using optically pumped NMR, revealing localized excitations and long relaxation times.

Contribution

It provides new insights into electron spin relaxation times and localization phenomena in quantum Hall systems through advanced NMR techniques.

Findings

Spin-reversed excitations are localized over ~40 microseconds.

Electron spin-lattice relaxation time ranges from 100 microseconds to 500 milliseconds.

Electron spin temperature can be driven above lattice temperature.

Abstract

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra provide evidence that spin-reversed charged excitations of the nu=1/3 ground state are localized over the NMR time scale of ~40 microseconds. Furthermore, by varying NMR pulse parameters, the electron spin temperature (as measured by the Knight shift) could be driven above the lattice temperature, which shows that the value of the electron spin-lattice relaxation time lies between 100 microseconds and 500 milliseconds at nu=1/3.