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O: Fachverband Oberflächenphysik

O 56: 2D Materials III: Growth, Structure and Substrate Interaction II (joint session O/CPP)

O 56.2: Talk

Wednesday, March 29, 2023, 15:15–15:30, GER 37

Electronic, chemical and structural properties of ultrathin Ta₂NiSe₅ flakes — •Kathrin Küster¹, Yuanshan Zhang¹, Dennis Huang¹, Ulrich Starke¹, and Hidenori Takagi^1,2,3 — ¹Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart, Germany — ²Institute for Functional Matter and Quantum Technologies, University of Stuttgart, 70569 Stuttgart, Germany — ³Department of Physics, University of Tokyo, 113-0033 Tokyo, Japan

The excitonic insulator is a theoretically proposed state of matter wherein a macroscopic condensate of electron-hole pairs, i.e., excitons, spontaneously forms below a transition temperature. The 2D-layered chalcogenide Ta₂NiSe₅ has arisen as a leading candidate of an excitonic insulator in a bulk crystal. Here we prepared ultrathin films (down to 2 nm) of Ta₂NiSe₅ and analyzed their structural, electronic and chemical properties with a NanoESCA (Scienta Omicron) on a local scale. Angle-resolved photoelectron spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS), together with photoelectron emission microscopy (PEEM) and imaging XPS give detailed insight into the thickness dependent properties of the flakes. By exposure to UV-light we observe a contrast change in the PEEM images which is caused by a strong modification of the work function of the flakes, which we tentatively relate to a phase transition of the Ta₂NiSe₅ flakes.