Hot carrier relaxation of Dirac fermions in bilayer epitaxial 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–Grüneisen power-law behaviour of T4 at carrier temperatures from 1.4 K up to ∼100 K, due to electron-acoustic phonon interactions with a deformation potential coupling constant of 22 eV. A carrier density dependence in the scaling of the T4 power law is observed in bilayer graphene, in contrast to the 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.