title: Tunable Ultrafast Thermal Relaxation in Graphene Measured by Continuous-Wave Photomixing.
abstract: Hot electron effects in graphene are significant because of graphene's small electronic heat capacity and weak electron-phonon coupling, yet the dynamics and cooling mechanisms of hot electrons in graphene are not completely understood. We describe a novel photocurrent spectroscopy method that uses the mixing of continuous-wave lasers in a graphene photothermal detector to measure the frequency dependence and nonlinearity of hot-electron cooling in graphene as a function of the carrier concentration and temperature. The method offers unparalleled sensitivity to the nonlinearity, and probes the ultrafast cooling of hot carriers with an optical fluence that is orders of magnitude smaller than in conventional time-domain methods, allowing for accurate characterization of electron-phonon cooling near charge neutrality. Our measurements reveal that near the charge neutral point the nonlinear power dependence of the electron cooling is dominated by disorder-assisted collisions, while at higher carrier concentrations conventional momentum-conserving cooling prevails in the nonlinear dependence. The relative contribution of these competing mechanisms can be electrostatically tuned through the application of a gate voltage-an effect that is unique to graphene.
authors.affiliation: Institute for Research in Electronics & Applied Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: M Mehdi
authors.initials: MM
authors.lastname: Jadidi
authors.affiliation: Institute for Research in Electronics & Applied Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Suess
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Cheng
authors.initials: C
authors.lastname: Tan
authors.affiliation: Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Xinghan
authors.initials: X
authors.lastname: Cai
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Andrei B
authors.initials: AB
authors.lastname: Sushkov
authors.affiliation: Institute for Research in Electronics & Applied Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Mittendorff
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.affiliation: Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: H Dennis
authors.initials: HD
authors.lastname: Drew
authors.affiliation: Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA.|School of Physics and Astronomy, Monash University, 3800 Victoria, Australia.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Fuhrer
authors.affiliation: Institute for Research in Electronics & Applied Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Murphy