Modeling the nonthermal relaxation processes of photoexcited solids: A short review

Abstract

Ultrafast electron dynamics of solids after an absorption of femtosecond laser pulse is governed by electron-electron, electron-phonon, phonon-electron, and phonon-phonon collisions. It is of importance to construct a framework for interpreting experimental observations correctly. In this paper we review recent developments of modeling the relaxation dynamics of solids. We discuss the ultrafast relaxation in respect to the effective temperature dynamics and the excess energy dynamics.

Accessing the anisotropic non-thermal phonon populations in black phosphorus

“…In combination with calculations of the onephonon structure factor and first-principles calculations of the microscopic couplings, this model successfully reproduces the time-dependent inelastic scattering maps and the phonon thermalization dynamics. In contrast to previous non-thermal lattice models for describing microscopic energy flow, where partitioning is based on the symmetry of phonons [20,22,41], we expect the notion of momentum-space partitioning introduced here to be an essential aspect of non-thermal lattice models for highly anisotropic crystals and composite materials like van der Waals heterostructures. This approach is fully transferable to near-equilibrium conditions as in thermal and electrical transport.…”

“…To investigate possible signatures of these phenomena on the FEIS signals, we define a phenomenological model of carrier thermalization, which explicitly accounts for the anisotropic scattering phase space in the BZ. In the two-temperature model (TTM) [37,38], and its generalization to multiple temperatures [20,[22][23][24][39][40][41], the temporal evolution of the electron and phonon distribution functions for a photoexcited system are determined via a set of coupled equations for the effective electron and phonon temperature, T el and T ph , respectively. Here, we generalize this model to account for momentum anisotropy of the initial electronic population.…”