Abstract
Conference Title: 2016 41st International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz) Conference Start Date: 2016, Sept. 25 Conference End Date: 2016, Sept. 30 Conference Location: Copenhagen, Denmark We study nonlinear THz effects in photoexcited gated graphene, using optical-pump/Zwtewse-THz-probe spectroscopy. A crossover from negative to positive differential THz transmission has been observed at the lowest doping concentration when the THz field is increased. Using a simple Drude model of the graphene photoconductivity, we attributed the observed behavior to a transition from a domain in which the increase in the Drude weight dominates over the increase in the scattering rate after photoexcitation, to a domain with the opposite properties when the THz probe field is increased.