Element-specific ultrafast lattice dynamics in monolayer WSe2

TL;DR

This study uses ultrafast electron diffraction to reveal element-specific lattice dynamics in monolayer WSe2, identifying energy transfer processes between phonon groups and long-lasting optical phonon overpopulation.

Contribution

It introduces a quantitative method to extract element-specific atomic vibrations in ultrafast dynamics, enabling detailed insight into lattice evolution in 2D materials.

Findings

Identification of stages in nonthermal lattice evolution

Detection of long-lasting optical phonon overpopulation

Element-specific vibrational information in ultrafast regime

Abstract

We study monolayer WSe2 using ultrafast electron diffraction. We introduce an approach to quantitatively extract atomic-site-specific information, providing an element-specific view of incoherent atomic vibrations following femtosecond excitation. Via differences between W and Se vibrations, we identify stages in the nonthermal evolution of the lattice. Combined with a calculated phonon dispersion, this element specificity enables us to identify a long-lasting overpopulation of specific optical phonons, and to interpret the stages as energy transfer processes between specific phonon groups. These results demonstrate the appeal of resolving element-specific vibrational information in the ultrafast time domain.