Stochastic scattering theory for excitation induced dephasing: Time-dependent nonlinear coherent exciton lineshapes

TL;DR

This paper introduces a stochastic theory for modeling excitation-induced dephasing in excitons, capturing many-body dynamics and Coulomb screening effects, validated through multidimensional spectroscopy on a semiconductor with strong excitonic interactions.

Contribution

The work develops a novel stochastic model that incorporates time-dependent exciton-exciton scattering and Coulomb screening, providing new insights into many-body effects on exciton lineshapes.

Findings

Dephasing slows over time due to many-body interactions.

Exciton lineshapes evolve from dispersive to absorptive features.

The model accurately reproduces experimental spectral dynamics.

Abstract

We develop a stochastic theory that treats time-dependent exciton-exciton s-wave scattering and that accounts for dynamic Coulomb screening, which we describe within a mean-field limit. With this theory, we model excitation-induced dephasing 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 on a two-dimensional metal-halide semiconductor that hosts tightly bound excitons and biexcitons that feature strong polaronic character. 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 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.