Coherent Spin Dynamics of Electrons and Holes Photogenerated with Large Kinetic Energy in Lead Halide Perovskite Crystals

Abstract

The coherent spin dynamics of electrons and holes are studied in a FA_0.9Cs_0.1PbI_2.8Br_0.2 perovskite bulk crystal using time-resolved Kerr ellipticity in a two-color pump–probe scheme. The probe photon energy is tuned to the exciton resonance, while the pump photon energy is detuned from it up to 0.75 eV to higher energies. The spin-oriented electrons and holes photogenerated with significant excess kinetic energy relax into states in the vicinity of the band gap, where they undergo Larmor precession in an external magnetic field. At cryogenic temperatures down to 1.6 K, the spin-dephasing time reaches the nanosecond range. During energy relaxation, the carrier spin relaxation is inefficient and only happens when the carriers become localized. In experiments with two pump pulses, all-optical control of the amplitudes and phases of the electron and hole spin signals is achieved in the additive regime by varying the intensities of the pump pulses and the time delay between them.