Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy

We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization ν∗_F of charge carriers in graphene. This allows the quantitative extraction of all electrical parameters (DC conductivity σ _DC, carrier density n, and carrier mobility µ) of large-scale graphene films placed on arbitrary substrates via THz-TDS. Particularly relevant are substrates with low relative permittivity (< 5) such as polymeric films, where notable renormalization effects are observed even at relatively large carrier densities (>10¹² cm^-2, Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical (σ _DC, n, µ) and electronic (ν∗_F) properties of large-scale graphene on generic substrates is key to utilize this material in applications such as metrology, flexible electronics as well as to monitor graphene transfers using polymers as handling layers.