Combination of Optical Transitions of Polarons with Rashba Effect in Methylammonium Lead Tri-halide Perovskites under High Magnetic Fields

TL;DR

This study explores how optical transitions in hybrid perovskites are affected by high magnetic fields, revealing complex behaviors linked to Rashba and polaron effects that vary with halogen composition.

Contribution

It introduces a novel explanation combining Rashba and polaron effects to understand magnetic field influences on perovskite photoluminescence transitions.

Findings

Different halogens show distinct PL energy shifts under magnetic fields.

The behavior of transition-energy shifts varies with halogen composition.

A proposed mechanism links Rashba and polaron effects to observed phenomena.

Abstract

We investigate photoluminescence (PL) transitions of MAPbX$_{3}$ (X = I, Br and Cl) organic-inorganic hybrid perovskite single crystals under magnetic fields of up to 60 T. In these materials, sharp free-exciton transition peaks emerge at a low temperature (4.2 K). Under strong magnetic fields, the free-exciton PL transitions of three different halogens show dramatic differences. The free-exciton transitions of the MAPbCl$_{3}$ crystal undergo negative energy shifts, while those of the MAPbBr$_{3}$ crystal show normal diamagnetic shifts. To obtain the variation from Cl to Br, we attempt to measure PL transitions of MAPbCl$_{x}$Br$_{3-x}$. For MAPbI$_{3}$, the transition-energy shifts for both $\sigma^{+}$ and $\sigma^{-}$ transitions at 4.2 K exhibit a power-law dependence on the magnetic field. Such inconsistent magnetic-field effects on different halogens make it difficult to understand the transition-energy behavior through a unified model. We propose a possible mechanism for the field effects that is based on a combination of the Rashba effect induced by strong spin-orbit coupling and the polaron effect caused by the polar nature of the inorganic elements.