title: Excitonic insulator state in Ta2NiSe5 probed by photoemission spectroscopy.
abstract: 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.
authors: Department of Physics, University of Tokyo, Kashiwa, Chiba 277-8561, Japan.
authors: Y
authors: Y
authors: Wakisaka
authors: T
authors: T
authors: Sudayama
authors: K
authors: K
authors: Takubo
authors: T
authors: T
authors: Mizokawa
authors: M
authors: M
authors: Arita
authors: H
authors: H
authors: Namatame
authors: M
authors: M
authors: Taniguchi
authors: N
authors: N
authors: Katayama
authors: M
authors: M
authors: Nohara
authors: H
authors: H
authors: Takagi