title: Microscopic description of intraband absorption in graphene: the occurrence of transient negative differential transmission.
abstract: We present a microscopic explanation of the controversially discussed transient negative differential transmission observed in degenerate optical pump-probe measurements in graphene. Our approach is based on the density matrix formalism allowing a time- and momentum-resolved study of carrier-light, carrier-carrier, and carrier-phonon interaction on microscopic footing. We show that phonon-assisted optical intraband transitions give rise to transient absorption in the optically excited hot carrier system counteracting pure absorption bleaching of interband transitions. While interband transition bleaching is relevant in the first hundreds of fs after the excitation, intraband absorption sets in at later times. In particular, in the low excitation regime, these intraband absorption processes prevail over the absorption bleaching resulting in a zero crossing of the differential transmission. Our findings are in good qualitative agreement with recent experimental pump-probe studies.
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.
authors.forename: Faris
authors.initials: F
authors.lastname: Kadi
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany and Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Torben
authors.initials: T
authors.lastname: Winzer
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.
authors.forename: Ermin
authors.initials: E
authors.lastname: Malic
authors.affiliation: Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Knorr
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Göttfert
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden, Germany and Technische Universität Dresden, 01062 Dresden, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Mittendorff
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Winnerl
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden, Germany and Technische Universität Dresden, 01062 Dresden, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Helm