We report temperature-dependent angle-resolved photoemission spectroscopy measurement of Ta 2NiSe 5 which shows a semiconductor- semiconductor structural phase transition at around 330 K. Characteristically, flat band at the top of the valence band is observed, which is ascribed to the excitonic insulator effect. The top valence band shifts to higher binding energy and its bandwidth increases as the temperature decreases. As the system exceeds the transition temperature, the flat feature of the valence band weakens though the exciton fluctuations remain finite.
- Excitonic insulator
- Layered chalcogenide
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics