Excitonic Insulator State inTa2NiSe5Probed by Photoemission Spectroscopy

著者: Yuki Wakisaka, Takaaki Sudayama, Kou Takubo, T. Mizokawa, Masashi Arita, H. Namatame, M. Taniguchi, Naoyuki Katayama, M. Nohara, H. Takagi - Physical Review Letters 2009 被引用: 311

We report on a photoemission study of Ta2NiSe5 that has a quasi-one-dimensional structure and an insulating ground state. Ni 2p core-level spectra show that the Ni 3d subshell is partially occupied and the Ni 3d states are heavily hybridized with the Se 4p states. In angle-resolved photoemission spectra, the valence-band top is found to be extremely flat, indicating that the ground state can be viewed as an excitonic insulator state between the Ni 3d-Se 4p hole and the Ta 5d electron. We argue that the high atomic polarizability of Se plays an important role to stabilize the excitonic state.