Ultrafast Relaxation of Excited Dirac Fermions in Epitaxial Graphene Using Optical Differential Transmission Spectroscopy (original) (raw)

Ultrafast dynamics and interlayer thermal coupling of hot carriers in epitaxial graphene

physica status solidi c, 2009

We report the first application of nondegenerate ultrafast pump‐probe spectroscopy to investigate the dynamics of hot Dirac Fermions in epitaxial graphene. The DT spectra can be understood in terms of the effect of hot thermal carrier distributions on interband transitions with no electron‐hole interaction. We also investigate the thermal coupling between carriers of doped and undoped layers. The coupling time is found to be below 500fs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier Relaxation in Epitaxial Graphene Photoexcited Near the Dirac Point

Physical Review Letters, 2011

We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 - 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical phonon frequency, however, owing to the presence of hot carriers, optical phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.

Ultrafast nonlinear optical response of Dirac fermions in graphene

Nature communications, 2018

The speed of solid-state electronic devices, determined by the temporal dynamics of charge carriers, could potentially reach unprecedented petahertz frequencies through direct manipulation by optical fields, consisting in a million-fold increase from state-of-the-art technology. In graphene, charge carrier manipulation is facilitated by exceptionally strong coupling to optical fields, from which stems an important back-action of photoexcited carriers. Here we investigate the instantaneous response of graphene to ultrafast optical fields, elucidating the role of hot carriers on sub-100 fs timescales. The measured nonlinear response and its dependence on interaction time and field polarization reveal the back-action of hot carriers over timescales commensurate with the optical field. An intuitive picture is given for the carrier trajectories in response to the optical-field polarization state. We note that the peculiar interplay between optical fields and charge carriers in graphene m...

Ultrafast Relaxation Dynamics of Hot Optical Phonons in Graphene

2009

Using ultrafast optical pump-probe spectroscopy, we study the relaxation dynamics of hot optical phonons in few-layer and multi-layer graphene films grown by epitaxy on silicon carbide substrates and by chemical vapor deposition on nickel substrates. In the first few hundred femtoseconds after photoexcitation, the hot carriers lose most of their energy to the generation of hot optical phonons which then present the main bottleneck to subsequent carrier cooling. Optical phonon cooling on short time scales is found to be independent of the graphene growth technique, the number of layers, and the type of the substrate. We find average phonon lifetimes in the 2.5-2.55 ps range. We model the relaxation dynamics of the coupled carrier-phonon system with rate equations and find a good agreement between the experimental data and the theory. The extracted optical phonon lifetimes agree very well with the theory based on anharmonic phonon interactions.