# Spin-polarized self-trapped excitons in low-dimensional cesium copper halide

## TL;DR

Researchers discovered a new type of spin-polarized exciton in a copper halide material that could improve spin-photonic devices.

## Contribution

The study introduces a naturally formed spin-polarized self-trapped exciton in cesium copper iodide with strong spin-exciton coupling and high emission efficiency.

## Key findings

- A self-trapped exciton in cesium copper iodide shows a giant Zeeman splitting of −53 meV and a high g-factor of −93.5.
- The material exhibits electroluminescence with 44.5% circular polarization at 4.2 K.
- Spin-optic properties of the copper compound suggest potential for next-generation spin-photonic devices.

## Abstract

Spin polarized excitons induced by spin injection from magnetic ion to a single quantum dot, has been considered as a basic unit of quantum information transfer between spin and photon for spin-photonic applications. However, this state-of-the-art technology has only been found with limited coupling strength and weak excitonic emission. Here, we demonstrate a spin-polarized self-trapped exciton naturally formed in the zero-dimensional lattice of cesium copper iodide. Upon excitation, the conversion from Cu+ ion to spin-1/2 Cu2+ ion results in an in-situ self-trapped exciton, which facilitates a local Jahn-Teller distortion and guarantees the strong spin-exciton coupling and near-unity excitonic emission efficiency. Consequently, a giant Zeeman splitting of −53 meV and an effective excitonic g-factor of −93.5 are observed from magneto-photoluminescence. More importantly, this nano-scale coupling can also be driven by an external electric field, which generates electroluminescence with a circular polarization of 44.5% at 4.2 K and 8% at 300 K. The spin-optic properties of this copper compound will stimulate the fabrication of next-generation spin-photonic devices based on self-trapped excitons.

Wannier excitons exhibit a relatively large Bohr radius, and this limits the strength of coupling to magnetic ions, in exciton hosting material. Here, Huang et al. overcome this limitation by using self-trapped excitons in Cs3Cu2I5, with a resulting large exciton Zeeman splitting.