Optical pumping of the electron spin polarization in bulk CuCl

TL;DR

This paper proposes a method for optical electronic spin pumping in bulk CuCl using resonant excitation of negatively charged excitons, achieving near 100% spin polarization in under 100 picoseconds.

Contribution

It introduces a new optical pumping mechanism based on the valence band structure of CuCl and models the dynamics using density matrix formalism coupled with Maxwell's equations.

Findings

Spin polarization close to 100% achievable

Polarization can be achieved in less than 100 ps

Model predicts efficient optical spin pumping in CuCl

Abstract

In CuCl bulk crystal negatively charged excitons (trions $X^-$) can be induced by the resonant optical excitation of extra electrons in conduction band minimum. In the case of light polarization and due to the top valence band structure of CuCl only the electrons with spin antiparallel to the direction of the light propagation contribute to the formation of $X^-$, while the emerging $X^-$ can recombine into both possible electron states, with spin parallel and antiparallel to the direction of light propagation. We propose to use this mechanism for optical electronic spin pumping. We describe the dynamics of pumping in terms of density matrix formalism. The coherent pumping laser pulse propagating through the sample is described by Maxwell wave equation coupled to the density matrix evolution equations. The results of our approximate simple model calculations suggest that spin polarization close to 100% can be achieved in time shorter than 100ps.