Calibrating Out-of-Equilibrium Electron–Phonon Couplings in Photoexcited MoS₂

Abstract

Nonequilibrium electron−phonon coupling (EPC) serves as a dominant interaction in a multitude of transient processes, including photoinduced phase transitions, coherent phonon generation, and possible light-induced superconductivity.Here we use monolayer MoS 2 as a prototype to investigate the variation in electron−phonon couplings under laser excitation, on the basis of real-time time-dependent density functional theory simulations. Phonon softening, anisotropic modification of the deformation potential, and enhancement of EPC are observed, which are attributed to the reduced electronic screening and modulated potential energy surfaces by photoexcitation. Furthermore, by tracking the transient deformation potential and nonthermal electronic population, we can monitor the ultrafast time evolution of the energy exchange rate between electrons and phonons upon laser excitation. This work provides an effective strategy to investigate the nonequilibrium EPC and constructs a scaffold for understanding nonequilibrium states beyond the multitemperature models.

Indirect Exciton–Phonon Dynamics in MoS2 Revealed by Ultrafast Electron Diffraction

“…As a result, the potential energy surface of the ground state becomes more flat and asymmetrical leading to a displaced equilibrium position following the photoexcitation (see Figure 4b). [ 37–39 ] Based on these considerations, we have then estimated for the different Bragg reflections the structure factor changes resulting from in‐plane and out‐of‐ plane displacements of S and Mo atoms following the direction of motion consistent with A 1 ′ and E ′ modes (see Figure 4c–e and Section S1 of Supporting Information).…”

Coherent Phonon‐Induced Modulation of Charge Transfer in 2D Hybrid Perovskites

“…[13,35] In contrast, FM would result from the oscillating energy levels due to the Fröhlich interaction of longitudinal optical phonons and deformation potential interaction of longitudinal acoustic phonons with charge carriers. [36][37][38][39][40][41] In simpler terms, the oscillating lattice deformations associated with the phonons modulate the energy of carriers in the lattice. In hybrid materials, this causes the energy levels at the interface of the organic and inorganic to shift periodically relative to one another, which can cause the carrier population to oscillate between the organic and inorganic components.…”

Photoinduced Ultrafast Phase Transition in Bilayer CrI3

“…In recent years, a new approach has emerged that allows in situ manipulation: driving systems out of equilibrium by irradiating them with light. The femtosecond laser technique has become an appealing approach to exploring ultrafast changes and manipulations of material properties owing to the recent advances in ultrafast time-resolved diffraction techniques that combine ultrafast temporal manipulation with atomic-scale spatial resolution. − The photoexcitation induces a nonequilibrium occupation of excited electronic states, which could lead to periodic lattice distortions and expose the transient metastable states. , This approach shows promising applications in demagnetization, inducing ferromagnetism, , enhancing magnetic exchange interactions, and manipulating magnetically ordered properties in two-dimensional materials. − …”

“…The maximum widths of the forbidden bands of the R-stacked and M-stacked BLC are 1.21 and 1.16 eV, respectively. Based on the semiconductor nature of BLC and previous works, − we simulated the real-time evolution of the structure and electronic states of the R-stacked BLC under a series of Gaussian light fields with a given frequency of ℏω = 1.55 eV and different electric field strengths. More comparisons of parameters are discussed in Note S1 of the Supporting Information.…”

“…The softening of the phonon modes basically scales with the density of photoexcited carriers. We further estimate the electron–phonon coupling matrix elements of these two phonon modes coupled with the valence band maximum and conduction band minimum, as shown in Note S5 of the Supporting Information . We found the enhancement effect of electron–phonon coupling under a light field, and the stronger electron–phonon coupling is more favorable for the occurrence of horizontal relative displacement between layers.…”