Hot carrier relaxation of Dirac fermions in bilayer epitaxial graphene

TL;DR

This study experimentally investigates hot carrier energy relaxation in bilayer epitaxial graphene, revealing a T^4 power-law behavior and a unique carrier density dependence, contrasting with monolayer graphene, and providing insights into graphene's hot carrier dynamics.

Contribution

It provides the first detailed experimental analysis of hot carrier relaxation in bilayer epitaxial graphene, highlighting differences from monolayer graphene and elucidating electron-phonon interactions.

Findings

Energy loss rate follows T^4 behavior up to 100 K.

Carrier density dependence of energy loss rate differs from monolayer graphene.

Electron-phonon relaxation time varies strongly with carrier density in bilayer graphene.

Abstract

Energy relaxation of hot Dirac fermions in bilayer epitaxial graphene is experimentally investigated by magnetotransport measurements on Shubnikov-de Haas oscillations and weak localization. The hot-electron energy loss rate is found to follow the predicted Bloch-Gr\"uneisen power-law behaviour of $T^4$ at carrier temperatures from 1.4 K up to $\sim$100 K, due to electron-acoustic phonon interactions with a deformation potential coupling constant of 22 eV. A carrier density dependence $n_e^{-1.5}$ in the scaling of the $T^4$ power law is observed in bilayer graphene, in contrast to the $n_e^{-0.5}$ dependence in monolayer graphene, leading to a crossover in the energy loss rate as a function of carrier density between these two systems. The electron-phonon relaxation time in bilayer graphene is also shown to be strongly carrier density dependent, while it remains constant for a wide range of carrier densities in monolayer graphene. Our results and comparisons between the bilayer and monolayer exhibit a more comprehensive picture of hot carrier dynamics in graphene systems.