Berlin 2015 – scientific programme
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O: Fachverband Oberflächenphysik
O 48: Graphene: Dynamics
O 48.9: 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 Gierz1 — 1MPI 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)