Gate-tunable ultrafast optical response of single-layer graphene

The ultrafast relaxation dynamics in single-layer graphene (SLG) is of key importance for its applications in optoelectronic devices which rely on the dynamic response of charge carriers, such as photodetectors, saturable absorbers and modulators[1]. The absorption via interband transitions of a photon of energy in ? SLG promotes an electron from an energy -?/2 in the valence band to an energy ?/2 in the conduction band. This strongly non-equilibrium distribution thermalizes by electron-electron scattering (t~ 10-20 fs) to a hot Fermi-Dirac (FD) distribution, which in turn equilibrates with the cold lattice via interaction with strongly-coupled optical phonons (SCOP, t~200-300 fs) and, on a longer time scale, via anharmonic coupling with acoustic phonons (t~ 1-2 ps) [2].