Spin-polarized exciton quantum beating in hybrid organic-inorganic perovskites

The hybrid organic-inorganic perovskites are an emerging class of semiconductors that have excellent optoelectronic properties, even being solution processed. These compounds also hold great promise for the field of spintronics due to their large and tunable spin-orbit coupling, spin-dependent optical selection rules, and predicted electrically tunable Rashba spin splitting. Here we demonstrate the optical orientation and quantum beating of spin-polarized excitons in polycrystalline films of MAPbCl_xI_3-x using a time-resolved Faraday rotation measurement [1]. The spin lifetime exceeds 1 ns in zero magnetic field at 4 K, which is quite surprising given that Pb and I exhibit large spin-orbit couplings. Application of a transverse magnetic field causes quantum beating at two distinct frequencies, and the approximate linear relationships give two g-factors, which we assign to electrons and holes as g_e = 2.63, and g_h = -0.33 according to an exciton model. The energy dependence of the Faraday rotation follows the exciton absorption band at low temperatures, confirming its excitonic origin. Spin relaxation mechanisms and unusual exciton spin physics will also be discussed.
[1] P. Odenthal et al., Nature Physics 13, 894–899 (2017)