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Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 62: Graphene: Dynamics (jointly with O, HL)

TT 62.9: Talk

Wednesday, March 18, 2015, 12:45–13:00, MA 041

Dirac carrier thermalization on the sub 10fs timescale observed by tr-ARPES — •Sven Aeschlimann1,2, Mariana Chavez Cervantes1, Francesca Calegari1,3, Cephise Cacho4, Emma Springate4, Stefan Link2, Ulrich Starke2, Klaus Kern2,5, Andrea Cavalleri1,6, Christian R. Ast2, and Isabella Gierz11MPI for the Structure and Dynamics of Matter, Hamburg, Germany — 2MPI for Solid State Research, Stuttgart, Germany — 3IFN, Consiglio Nazionale delle Ricerche, Milano, Italy — 4Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell, United Kingdom — 5EPFL, Lausanne, Switzerland — 6University of Oxford, United Kingdom

We used time- and angle-resolved photoemission spectroscopy (tr-ARPES) with extreme ultra-violet (XUV) probe pulses from high order harmonics generation (HHG) to observe the ultrafast electron dynamics in photo-excited quasi-freestanding epitaxial graphene monolayers. By the use of the hollow core fiber compression technique, we produced 8 fs pulses, which are utilized both for driving HHG and for photo-excitation. These ultrashort pulses allowed us to observe the initial thermalization of photo-excited carriers via electron-electron scattering with unprecedented temporal resolution. We find that, at early times, the carrier distribution neither follows a Fermi-Dirac distribution nor the non-equilibrium distribution expected for a population-inverted state [1]. We attribute this to the short duration of the pump pulse on the order of the electron-electron scattering time.

[1] I. Gierz et al., Nature Materials 12, 1119 (2013)

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