Giant optical orientation of exciton spins in lead halide perovskite crystals

TL;DR

This paper demonstrates near-unity optical orientation of exciton spins in lead halide perovskite crystals, revealing strong spin polarization and suppressed relaxation, with implications for spintronics and quantum information.

Contribution

It reports the first observation of nearly complete optical orientation of exciton spins in lead halide perovskites, showing robust spin polarization even with large excitation detuning.

Findings

Optical orientation reaches 85%, close to the theoretical maximum.

Exciton spin lifetime is about 60 ps, distinguishable from electron-hole recombination.

Spin polarization persists with excitation detuning up to 0.5 eV.

Abstract

Optical orientation of carrier spins by circularly polarized light is the basis of spin physics in semiconductors. Here, we demonstrate strong optical orientation of 85\%, approaching the ultimate limit of unity, for excitons in FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$ lead halide perovskite bulk crystals. Time-resolved photoluminescence allows us to distinguish excitons with 60~ps lifetime from electron-hole recombination in the spin dynamics detected via coherent spin quantum beats in magnetic field. We reveal electron-hole spin correlations through linear polarization beats after circularly polarized excitation. Detuning of the excitation energy from the exciton resonance up to 0.5~eV does not reduce the optical orientation, evidencing clean chiral selection rules in agreement with atomistic calculations, and suppressed spin relaxation of electrons and holes even with large kinetic energies.