We quantify the role of many-body elastic scattering effects on exciton dephasing rates in two-dimensional hybrid metal-halide perovskites by means of nonlinear coherent excitation spectroscopy at a temperature of 5 K. We find that the exciton-density dependence of excitation-induced dephasing (EID) is two to three orders of magnitude lower than in other atomic monolayer semiconductors such as transition metal dichalchogenides. Furthermore, EID is different for the multiple excitons evident in the excitation line shape, as is their phonon-mediated temperature dependence. We ascribe these observations to screening effects due to polaronic dressing by the lattice. Furthermore, we develop a stochastic theory that treats time-dependent exciton–exciton <i>s</i>-wave scattering and that accounts for dynamic Coulomb screening, which we describe within a mean-field limit. With this theory, we model EID effects on time-resolved two-dimensional coherent optical lineshapes and we identify a number of features that can be attributed to the many-body dynamics occurring in the background of the exciton, including dynamic line narrowing, mixing of real and imaginary spectral components, and multi-quantum states. We test the model by means of multidimensional coherent spectroscopy. We find that the exciton nonlinear coherent lineshape reflects many-body correlations that give rise to excitation-induced dephasing. Furthermore, we observe that the exciton lineshape evolves with the population time over time windows in which the population itself is static in a manner that reveals the evolution of the multi-exciton many-body couplings. Specifically, the dephasing dynamics slow down with time, at a rate that is governed by the strength of exciton many-body interactions and on the dynamic Coulomb screening potential. The real part of the coherent optical lineshape displays strong dispersive character at zero time, which transforms to an absorptive lineshape on the dissipation timescale of excitation-induced dephasing effects, while the imaginary part displays converse behavior. Our microscopic theoretical approach is sufficiently flexible to allow for a wide exploration of how system-bath dynamics contribute to linear and non-linear time-resolved spectral behavior.

Many-body elastic scattering of exciton polarons in two-dimensional hybrid metal-halide perovskites

ACS Spring Meeting 2021

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