Berlin 2018 – scientific programme
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O: Fachverband Oberflächenphysik
O 12: Ultrafast Electron and spin dynamics at interfaces II
O 12.1: Talk
Monday, March 12, 2018, 15:00–15:15, MA 005
Excited states mapping of a transition metal dichalcogenide semiconductor — Michele Puppin1, 2, Chris Nicholson1, Adriel Domínguez García3, Hannes Huebener3, Angel Rubio3, Laurenz Rettig1, Martin Wolf1, and •Ralph Ernstorfer1 — 1Fritz-Haber Institut, Berlin Germany — 2École polytechnique fédérale de Lausanne, Lausanne Switzerland — 3Max Planck Institut for the dynamics of matter, Hamburg, Germany
Time-resolved photoemission combined with scanning of the emission angle can extend established band-structure mapping to excited states which are only occupied out-of-equilibrium. The full potential of time- and angle-resolved photoemission spectroscopy (trARPES) is reached by performing the experiment at high repetition rates of hundreds of kHz, limiting space charge effects and data acquisition time. Extreme ultraviolet (XUV) photon energies grant access to the whole Brillouin zone: by performing high-harmonic generation at 0.5 MHz with a novel laser light source, we demonstrate trARPES with a photon energy of 21 eV, ≈100 meV resolution and sub-50 fs time resolution. A 3.1 eV pump pulse populates the conduction band of the layered transition metal dichalcogenide WSe2 followed by relaxation toward the band minimum within 1 picosecond. About 100 fs after excitation, most of the normally unoccupied conduction band states are populated due to scattering of the photo-excited carriers, allowing excited state band mapping throughout the whole Brillouin zone.