Probing photocarrier dynamics of pressurized graphene using time-resolved terahertz spectroscopy

Graphene hosts intriguing photocarrier dynamics such as negative transient terahertz (THz) photoconductivity, high electron temperature, benefiting from the unique linear Dirac dispersion. In this work, the pressure effects of photocarrier dynamics of graphene have been investigated using in situ time-resolved THz spectroscopy in combination with diamond anvil cell exceeding 9 GPa. We find that the negative THz conductivity maintains in our studied pressure range both for monolayer and bilayer graphene. In particular, the amplitude of THz photoconductivity in monolayer graphene manifests an extraordinary dropping with pressure, compared with that from the counterparts such as bulk silicon and bilayer graphene. Concomitantly, the time constant is reduced with increasing pressure, highlighting the pressure-induced hot carrier cooling. The pressure dependence of photocarrier dynamics in monolayer graphene is likely related with the enhancement of the interfacial coupling between diamond surface and sample, allowing for the activity of new electron-phonon scattering. Our work is expected to provide an impetus for the studies of high-pressure THz spectroscopy of two-dimensional materials.