Hot carrier dynamics and electron-optical phonon coupling in photoexcited graphene via time-resolved ultrabroadband terahertz spectroscopy

TL;DR

This study uses time-resolved ultrabroadband terahertz spectroscopy and simulations to analyze hot carrier dynamics and electron-optical phonon coupling in photoexcited graphene, revealing a slightly enhanced EPC due to electron-electron interactions.

Contribution

It provides the first experimental estimation of the EPC matrix element in graphene considering e-e interaction effects using THz spectroscopy and numerical modeling.

Findings

Observed negative photoconductivity at high pump fluence.

Estimated EPC matrix element near the K point as approximately 0.09.

Revealed that e-e interactions slightly enhance the EPC beyond theoretical predictions.

Abstract

Electron-electron (e-e) interaction is known as a source of logarithmic renormalizations for Dirac fermions in quantum field theory. The renormalization of electron--optical phonon coupling (EPC) by e-e interaction, which plays a pivotal role in hot carrier and phonon dynamics, has been discussed after the discovery of graphene. We investigate the hot carrier dynamics and the EPC strength using time-resolved ultrabroadband terahertz (THz) spectroscopy combined with numerical simulation based on the Boltzmann transport equation and comprehensive temperature model. The large negative photoconductivity and the non-Drude behavior of THz conductivity spectra appear under high pump fluence and can be attributed to the temporal variation of the hot carrier distribution and scattering rate. We successfully estimate the dimensionless EPC matrix element of the $A_1^{\prime}$ optical phonon mode near the $\mathbf{K}$ point as $\lambda_{\mathbf{K}} \approx$0.09 from the fitting of THz conductivity spectra and temporal evolution of transient THz reflectivity, which is slightly larger than the prediction of the renormalization group.