Simultaneous measurements of nuclear spin heat capacity, temperature and relaxation in GaAs microstructures

TL;DR

This study investigates the nuclear spin heat capacity in GaAs microstructures, confirming that quadrupole interactions induced by residual strain significantly enhance heat storage, impacting NSS cooling efficiency.

Contribution

It provides experimental validation that quadrupole interactions due to strain increase nuclear spin heat capacity in GaAs, using combined relaxation and NMR measurements.

Findings

Quadrupole splitting plays a key role in NSS heat storage.

Residual strain influences electric field gradients in GaAs.

Nuclear magnetization detected via electron spin noise spectroscopy.

Abstract

Heat capacity of the nuclear spin system (NSS) in GaAs-based microstructures has been shown to be much greater than expected from dipolar coupling between nuclei, thus limiting the efficiency of NSS cooling by adiabatic demagnetization. It was suggested that quadrupole interaction induced by some small residual strain could provide this additional reservoir for the heat storage. We check and validate this hypothesis by combining nuclear spin relaxation measurements with adiabatic remagnetization and nuclear magnetic resonance experiments, using electron spin noise spectroscopy as a unique tool for detection of nuclear magnetization. Our results confirm and quantify the role of the quadrupole splitting in the heat storage within NSS and provide additional insight into fundamental, but still actively debated relation between a mechanical strain and the resulting electric field gradients in GaAs.