Anisotropic Carrier Dynamics in Graphite/Graphene Probed with Time-and Angle-Resolved Photoemission Spectroscopy*

Most HHG-based ARPES have suffered from severe restrictions imposed by space-charge limits and low collection efficiency of the photoelectrons from low repetition rates. These restrictions have largely precluded the study of the intrinsic dynamics of excited states in weakly excited systems. At Stony Brook, we have developed a tunable high rep-rate HHG source operating at 61 MHz in the range 8 to 40 eV. Combining with a time-of-flight momentum microscopy enables rapid time-resolved ARPES measurements with coverage of the full Brillouin zone in the perturbative excitation limit. In this work, we will discuss measurements of polarization dependent anisotropic distribution of excited electrons in HOPG graphite and monolayer graphene. We will discuss how different pump polarizations and probed photon energies affect this anisotropic angular distribution in all K/K’ in incident pump fluence ranging from 1 to 80 μJ/cm². We compare our measurements to a theory[1] that includes both electron-electron and electron-phonon scattering.

 

[1] E. Malic, T. Winzer, E. Bobkin and A. Knorr,  Physical Review B, 84(20), 205406 (2011).