Light-induced nuclear quadrupolar relaxation in semiconductors

TL;DR

This paper reveals a new light-induced nuclear relaxation mechanism in semiconductors caused by modulation of the quadrupolar Hamiltonian due to photoelectron trapping, significantly affecting nuclear polarization.

Contribution

It introduces a novel relaxation process involving quadrupolar interactions modulated by photoelectrons, expanding understanding of nuclear spin dynamics under illumination.

Findings

Light excitation causes nuclear depolarization via quadrupolar relaxation.

Nuclear magnetization can decrease by over an order of magnitude.

The process is significant near shallow donors with partial photoelectron occupation.

Abstract

Light excitation of a semiconductor, known to dynamically-polarize the nuclear spins by hyperfine contact interaction with the photoelectrons, also generates an intrinsic nuclear depolarization mechanism. This novel relaxation process arises from the modulation of the nuclear quadrupolar Hamiltonian by photoelectron trapping and recombination at nearby localized states. For nuclei near shallow donors, the usual diffusion radius is replaced by a smaller, quadrupolar, radius. If the light excitation conditions correspond to partial donor occupation by photoelectrons, the nuclear magnetization and the nuclear field can be decreased by more than one order of magnitude.