Millisecond-long electron spin lifetime in CsPbI$_3$ perovskite nanocrystals revealed by optically detected magnetic resonance

TL;DR

This study reveals that electron spins in CsPbI3 perovskite nanocrystals can have millisecond-long relaxation times at low temperatures, using advanced magnetic resonance techniques to understand spin dynamics and relaxation mechanisms.

Contribution

The paper introduces a resonant spin inertia technique to measure electron and hole spin relaxation times in perovskite nanocrystals, providing new insights into their spin relaxation mechanisms.

Findings

Electron spin relaxation time T1 reaches 0.9 ms at 1.6 K.

Nuclear spin bath has a correlation time of about 60 μs.

Spin relaxation is explained by a two-LO-phonon Raman process.

Abstract

Perovskite nanocrystals are a convenient model system for optical spin orientation and manipulation. However, its real potential might be underestimated due to the incomplete knowledge on spin relaxation times, which are obscured by the limited sensitivity of measurement techniques as well as by the insufficient understanding of the spin relaxation mechanisms in perovskites. In this work, we study the spin relaxation of charge carriers in perovskite nanocrystals both experimentally and theoretically. We address the electron and hole spins in CsPbI$_3$ nanocrystals embedded in a glass matrix by the resonant spin inertia technique based on optically detected magnetic resonance. It allows us to determine the longitudinal spin relaxation time $T_1$ separately for electrons and holes, the $g$ factors, and the effective Overhauser field of the nuclear spin bath. At a temperature of 1.6 K, the $T_1$ time for electrons can be as long as 0.9 ms. We reveal the effect of the time-varying nuclear field fluctuations, which enhances the electron spin relaxation at low magnetic fields, and measure a rather long nuclear spin correlation time of about 60 $\mu$s. We develop a model of the spin relaxation in nanocrystals based on a two-LO-phonon Raman process, which explains the observed temperature dependence of the time $T_1$.