Nonlinear intensity dependence of terahertz edge photocurrents in graphene

Abstract

We report on the observation of terahertz radiation induced edge photogalvanic currents in graphene, which are nonlinear in intensity. The increase of the radiation intensities up to MW/cm 2 results in a complex nonlinear intensity dependence of the photocurrent. The nonlinearity is controlled by the back gate voltage, temperature and radiation frequency. A microscopic theory of the nonlinear edge photocurrent is developed. Comparison of the experimental data and theory demonstrates that the nonlinearity of the photocurrent is caused by the interplay of two mechanisms, i.e. by direct inter-band optical transitions and Drude-like absorption. Both photocurrents saturate at high intensities, but have different intensity dependencies and saturation intensities. The total photocurrent shows a complex sign-alternating intensity dependence. The functional behaviour of the saturation intensities and amplitudes of both kinds of photogalvanic currents depending on gate voltages, temperature, radiation frequency and polarization is in a good agreement with the developed theory.

Highly superlinear photogalvanic effects in (Bi$_{0.3}$Sb$_{0.7}$)$_2$(Te$_{0.1}$Se$_{0.9}$)$_3$: Probing 3D topological insulator surface states at room temperature

“…5 and 6 where the data for all samples are presented in double-logarithmic presentation. While such a dependence may in principle be described in terms of two-photon absorption, our estimation shows that in the mid infrared range such transitions will yield considerable contributions only for intensities by many orders of magnitude larger as those used in our work [35]. At the same time, the observed superlinearity can be explained for any level of the radiation intensities by considering the redistribution of carriers in the energy space which results from the radiation-induced electron gas heating.…”

“…linearly with radiation intensity I [7][8][9]. Deviations from this linearity have been observed in quantum wells [33,34] and in graphene [35] and their analysis opened up new opportunities for materials characterization. In TIs, however, the presence of such effects has neither experimentally nor theoretically been addressed.…”