Combination of optical transitions of polarons with Rashba effect in methylammonium lead trihalide perovskites under high magnetic fields

We investigate photoluminescence (PL) transitions of (, 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 crystal undergo negative energy shifts, while those of the crystal show normal diamagnetic shifts. To obtain the variation from Cl to Br, we attempt to measure PL transitions of . For , the transition-energy shifts for both and 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.