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.
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