Dresden 2017 – scientific programme
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O: Fachverband Oberflächenphysik
O 70: 2D Materials Beyond Graphene III
O 70.9: Talk
Wednesday, March 22, 2017, 12:30–12:45, WIL A317
Intervalley scattering dynamics in MoS2 imaged by two-photon photoemission with a high-harmonic probe — •Robert Wallauer, Johannes Reimann, Nico Armbrust, Jens Guedde, and Ulrich Hoefer — Fachbereich Physik und Zentrum für Materialwissenschaften Philipps-Universität, 35032 Marburg, Germany
We will report on the application of time- and angle-resolved two-photon photoemission (2PPE) with a high-harmonic probe for the investigation of the electron dynamics of MoS2 in momentum space. For this purpose, we combined a high-repetition rate high-harmonic source with tunable femtosecond pump pulses and a 3D (kx, ky, E) electrostatic electron spectrometer. At our high-harmonic photon energy of 23.5 eV we essentially probe only the first layer, which is not necessarily equal to a bulk sample.
We used this setup to study the electron dynamics in the conduction band of MoS2 after optical excitation with different pump photon energies. Thereby we showed that optical excitation above the A exciton resonance at 1.8 eV with 2.05 eV pump pulses results in an immediate occupation of the conduction band at K followed by an ultrafast transfer to the conduction band minimum at Σ [1]. Subsequently, the occupation at both high-symmetry points decays slowly on a ps timescale. We will present new data for pump photon energies in the range of 1.8 - 2.1 eV and show how the dynamics of this transfer depend on the excess energy above the exciton resonance.
[1] R. Wallauer et al., Appl. Phys. Lett. 109, 162102 (2016).