A. J. Frenzel, C. H. Lui, W. Fang, N. L. Nair, P. K. Herring, P. Jarillo-Herrero, J. Kong, N. Gedik
When light is absorbed by a semiconductor, photoexcited charge carriers enhance the absorption of far-infrared radiation due to intraband scattering. We observe the opposite behavior in monolayer graphene, a zero-gap semiconductor with lin- ear dispersion. By using time domain terahertz (THz) spectroscopy in conjunction with optical pump excitation, we observe a reduced absorption of THz radiation in photoexcited graphene. The measured spectral shape of the differential optical conductivity exhibits strongly non-Drude behavior. We discuss the influence of hot optical phonons, thermally broadened carrier distribution, and stimulated emission of THz radiation on the low-frequency non-equilibrium optical response of graphene.
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http://arxiv.org/abs/1301.6108
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