Nonlinear Magnetic Field Dependence of Quantum Beats in FAPbI₃

We present evidence for the magnetic field dependence of the electron and hole Landé g-factors in films of the hybrid organic–inorganic perovskite formamidinium lead iodide HC(NH2)2PbI3 (FAPI). We perform transient pump–probe Kerr spectroscopy on FAPI in magnetic fields up to 25 T, which reveals a significant deviation from the expected linear dependence of the quantum beating frequency on the applied magnetic field. We also found a decrease of the quantum beating frequencies with increasing pump intensity for a fixed magnetic field. These observations are discussed in terms of the dependence of the electron and hole Landé g-factors on the band gap, within a simple model in which the effective band gap increases at high magnetic field due to Landau level formation and increases with increasing pump intensity by virtue of shifts in the quasi-Fermi levels.