Circular dichroism in non-chiral metal halide perovskites

TL;DR

This paper theoretically shows that non-chiral metal halide perovskites can exhibit circular dichroism due to Rashba effects and symmetry breaking, enabling polarization-dependent light absorption without chiral molecules or magnetic fields.

Contribution

It introduces a novel mechanism for circular dichroism in non-chiral perovskites based on helical excitonic states and Rashba spin effects, expanding understanding of optical properties in these materials.

Findings

Significant CD with up to 30% anisotropy factor in orthorhombic perovskites.

CD arises from Rashba splitting and symmetry breaking effects.

Potential for observing CD in non-chiral perovskite structures.

Abstract

We demonstrate theoretically that non-chiral perovskite layers can exhibit circular dichroism (CD) in the absence of a magnetic field and without chiral activation by chiral molecules. The effect is shown to be due to splitting of helical excitonic states which can form in structures of orthorhombic or lower symmetry that exhibit Rashba spin effects. The selective coupling of these helical exciton states to helical light is shown to give rise to circular dichroism. Polarization dependent absorption is shown to occur due to the combined effect of Rashba splitting, in-plane symmetry breaking, and the effect of the exciton momentum on its fine structure, which takes the form of Zeeman splitting in an effective magnetic field. We calculate significant CD with an anisotropy factor of up to 30% in orthorhombic perovskite layers under off-normal top illumination conditions, raising the possibility of its observation in non-chiral perovskite structures.