Oscillatory Magnetic Circular Dichroism of Free-Carrier Absorption and Determination of the Rashba Dispersions in Hybrid Organic-Inorganic Perovskites.

Free-carrier absorption (FCA) in a semiconductor provides information about the band on which the free carriers reside, and in the classical limit, follows the ω-2 law with ω being the photon frequency. In hybrid organic-inorganic perovskites (HOIPs), the colossal Rashba effect (RE) results in a new band dispersion, characterized by wavevector |k| = k0 of band extremum and effective mass m*. Here we show that the colossal RE in two-dimensional HOIPs greatly enhances phonon-assisted FCA with a modified frequency dependence and induces a direct transition between the subbands with a resonance at ℏω = 4R ≡ 2ℏ2k02/m*, which, under a magnetic field, exhibits a strong oscillatory magnetic circular dichroism (MCD). The MCD spectrum allows a complete and reliable determination of k0 and m* for conduction and valence bands in HOIPs and helps reveal the microscopic mechanism of their outstanding photovoltaic performance.