Spin-Dependent Exciton–Exciton Interactions in a Mixed Lead Halide Perovskite Crystal

Abstract

We investigate the two-pulse photon echo response of excitons in the mixed lead halide perovskite crystal FA0.9Cs0.1PbI2.8Br0.2 in dependence on the excitation intensity and polarization of the incident laser pulses. Using spectrally narrow picosecond laser pulses, we address localized excitons with long coherence times T 2 ≈ 100 ps. This approach offers high sensitivity for the observation of excitation-induced changes in the homogeneous line width Γ2 = 2ℏ/T 2 on the μeV scale. Through intensity-dependent measurements, we evaluate the increase of Γ2 by 10 μeV at an exciton density of 1017 cm–3 being comparable with the intrinsic line width of 14 μeV. We observe that the decay of the photon echo and its power dependence are sensitive to the polarization configuration of the excitation pulses, which indicates that spin-dependent exciton–exciton interactions contribute to excitation-induced dephasing. In cross-linear polarization, the decay is faster and its dependence on exciton density is stronger as compared to the copolarized configuration. Using a two-exciton model accounting for different spin configurations we are able to reproduce the experimental results.