Chiral Symmetry and Electron Spin Relaxation of Lithium Donors in Silicon

TL;DR

This study combines theoretical predictions and experimental measurements to show that lithium donors in silicon exhibit extremely long electron spin relaxation times below 0.3 K due to chiral symmetry, with new mechanisms explaining observed kinetics.

Contribution

The paper introduces the concept of chiral symmetry in Li donor states in silicon and demonstrates its impact on spin relaxation times, supported by both theory and experiments.

Findings

Spin relaxation times are extremely long below 0.3 K.

Experimental magnetization kinetics agree with theoretical predictions.

A new spin decoherence mechanism involving off-site displacement and umklapp phonons is proposed.

Abstract

We report theoretical and experimental studies of the longitudinal electron spin and orbital relaxation time of interstitial Li donors in $^{28}$Si. We predict that despite the near-degeneracy of the ground-state manifold the spin relaxation times are extremely long for the temperatures below 0.3 K. This prediction is based on a new finding of the chiral symmetry of the donor states, which presists in the presence of random strains and magnetic fields parallel to one of the cubic axes. Experimentally observed kinetics of magnetization reversal at 2.1 K and 4.5 K are in a very close agreement with the theory. To explain these kinetics we introduced a new mechanism of spin decoherence based on a combination of a small off-site displacement of the Li atom and an umklapp phonon process. Both these factors weakly break chiral symmetry and enable the long-term spin relaxation.