Metal halide perovskites exhibit a materials physics that is distinct from traditional inorganic and organic semiconductors. While materials such as CH3NH3PbI3 are non-magnetic, the presence of heavy elements (Pb and I) in a non-centrosymmetric crystal environment result in a significant spin-splitting of the frontier electronic bands through the Rashba-Dresselhaus effect. We show, from a combination of \textit{ab initio} molecular dynamics, density-functional theory, and relativistic quasi-particle \textit{GW} theory, that the nature (magnitude and orientation) of the band splitting depends on the local asymmetry around the Pb and I sites in the perovskite structure. The potential fluctuations vary in time as a result of thermal disorder and a dynamic lone pair instability of the Pb(II) 6s26p0 ion. We show that the same physics emerges both for the organic-inorganic CH3NH3PbI3 and the inorganic CsPbI3 compound. The results are relevant to the photophysics of these compounds and are expected to be general to other lead iodide containing perovskites.
@article{arxiv.1711.00533,
title = {Dynamic Symmetry Breaking and Spin Splitting in Metal Halide Perovskites},
author = {Scott McKechnie and Jarvist M. Frost and Dimitar Pashov and Pooya Azarhoosh and Aron Walsh and Mark van Schilfgaarde},
journal= {arXiv preprint arXiv:1711.00533},
year = {2018}
}