Field-induced spin splitting and anomalous photoluminescence circular polarization in C H 3 N H 3 Pb I 3 films at high magnetic field

The organic-inorganic hybrid perovskites show excellent optical and electrical properties for photovoltaic and a myriad of other optoelectronics applications. Using high-field magneto-optical measurements up to 17.5 T at cryogenic temperatures, we have studied the spin-dependent optical transitions in the prototype $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{I}}_{3}$, which are manifested in the field-induced circularly polarized photoluminescence emission. The energy splitting between left and right circularly polarized emission bands is measured to be \ensuremath{\sim}1.5 meV at 17.5 T, from which we obtained an exciton effective $g$ factor of \ensuremath{\sim}1.32. Also from the photoluminescence diamagnetic shift we estimate the exciton binding energy to be \ensuremath{\sim}17 meV at low temperature. Surprisingly, the corresponding field-induced circular polarization is ``anomalous'' in that the photoluminescence emission of the higher split energy band is stronger than that of the lower split band. This ``reversed'' intensity ratio originates from the combination of long electron spin relaxation time and hole negative $g$ factor in $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{I}}_{3}$, which are in agreement with a model based on the k\ifmmode\cdot\else\textperiodcentered\fi{}p effective-mass approximation.