Spin-Electric Coupling in Lead Halide Perovskites

TL;DR

This paper investigates the electromagnetic interactions in lead-halide perovskites, revealing that spin-electric coupling is essential for accurately describing Faraday rotation and refractive index, surpassing minimal coupling models.

Contribution

It introduces a spin-electric coupling mechanism at the atomic level, improving the theoretical understanding of electromagnetic responses in lead-halide perovskites.

Findings

Spin-electric coupling explains experimental optical data.

Faraday effect is dominated by Zeeman splitting.

Beyond-Becquerel contributions are significant.

Abstract

Lead-halide perovskites enjoy a number of remarkable optoelectronic properties. To explain their origin, it is necessary to study how electromagnetic fields interact with these systems. We address this problem here by studying two classical quantities: Faraday rotation and the complex refractive index in a paradigmatic perovskite CH$_3$NH$_3$PbBr$_3$ in a broad wavelength range. We find that the minimal coupling of electromagnetic fields to the k$\cdot$p Hamiltonian is insufficient to describe the observed data even on the qualitative level. To amend this, we demonstrate that there exists a relevant atomic-level coupling between electromagnetic fields and the spin degree of freedom. This spin-electric coupling allows for quantitative description of a number of previous as well as present experimental data. In particular, we use it here to show that the Faraday effect in lead-halide perovskites is dominated by the Zeeman splitting of the energy levels, and has a substantial beyond-Becquerel contribution. Finally, we present general symmetry-based phenomenological arguments that in the low-energy limit our effective model includes all basis coupling terms to the electromagnetic field in the linear order.