Field-induced negative differential spin lifetime in silicon

TL;DR

This paper demonstrates that high electric fields in silicon cause a counterintuitive decrease in spin polarization, revealing a new spin relaxation mechanism involving phonon emission and valley scattering that challenges standard theories.

Contribution

It introduces a novel understanding of spin relaxation in silicon under electric fields, highlighting a field-induced negative spin lifetime due to phonon-assisted valley scattering.

Findings

Spin depolarization exceeds standard Elliott-Yafet predictions at low temperatures.

High electric fields induce a negative spin lifetime phenomenon.

Phonon emission during valley scattering is key to the observed effects.

Abstract

We show that the electric field-induced thermal asymmetry between the electron and lattice systems in pure silicon substantially impacts the identity of the dominant spin relaxation mechanism. Comparison of empirical results from long-distance spin transport devices with detailed Monte-Carlo simulations confirms a strong spin depolarization beyond what is expected from the standard Elliott-Yafet theory already at low temperatures. The enhanced spin-flip mechanism is attributed to phonon emission processes during which electrons are scattered between conduction band valleys that reside on different crystal axes. This leads to anomalous behavior, where (beyond a critical field) reduction of the transit time between spin-injector and spin-detector is accompanied by a counterintuitive reduction in spin polarization and an apparent negative spin lifetime.