Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 79: Poster: Ultrafast Electron and Spin Dynamics at Interfaces

O 79.10: Poster

Wednesday, March 14, 2018, 18:15–20:30, Poster A

Photoexcitation of doublons in 1T-TaS₂ — •Y. Beyazit¹, J. Beckord¹, I. Avigo¹, M. Ligges¹, M. Kalläne², P. Zhou¹, K. Rossnagel², and U. Bovensiepen¹ — ¹Faculty of Physics, University of Duisburg-Essen, Duisburg, Germany — ²Institute of Experimental and Applied Physics, University of Kiel, 24098 Kiel, Germany

Layered two-dimensional materials such as transition metal dichalcogenides exhibit rich phase diagrams. 1T-TaS₂ is metallic at high temperatures, while below 180 K it becomes an insulator and the topmost electronic band splits due to a commensurate periodic lattice distortion into an occupied lower (LHB) and an unoccupied upper Hubbard band (UHB), separated by a 350 meV energy gap. The UHB can be populated by generating doublons with femtosecond laser pulses whose photon energy (1.55 eV) largely exceeds the electronic band gap, raising questions on the underlying excitation mechanism [2-4]. Using femtosecond time- and angle-resolved photoemission with different pump photon energies we find that upon excitation with 1.55 eV photons the UHB is observed, pumping with 0.92 eV and 1.04 eV results in a suppression of the UHB signature. We conclude that for the generation of a doublon population in the UHB a resonant dipole transition from an initial state is required, which is not the case for pumping with the lower photon energy. This confirms a dipole-like excitation scheme proposed recently [4].

[1] Sipos et al., Nature Mater. 7, 960 (2008), [2] M. Ligges et al., arXiv:1702.05300 (2017), [3] N. ten Brinke et al., PRB 95, 195123 (2017), [4] A. Mann et al., PRB 94,115122 (2016)