Odd-to-Even-Layer Switch of Spontaneous Excitonic State in TiSe2 Thin Films
Abstract
TiSe2 is a candidate of high temperature excitonic condensates with spontaneous exciton formation in addition to its charge density wave (CDW). However, direct observation and manipulation of this electron-hole paring state formation is still lacking. Here, using varying-temperature angle-resolved photoemission spectroscopy (VT-ARPES), we observe a distinct odd-to-even-layer switch of spontaneous exciton state formation with the evident correlated band structure in TiSe2 thin films. While the odd-layer TiSe2 films show a sharp band structure in single-particle picture superimposed by CDW renormalization, in the even-layer TiSe2 films, the full-filling valence band (VB) opens a distinct notch at the top, and the conductive band (CB) shows a significant extra signal extending above Fermi level with spectra broadening. These features indicate that the extra holes (notched VB) and electrons (broadening CB above Fermi level) form spontaneous excitons in even-layer TiSe2. Based on a correlated electron-hole model extracted from the tight-binding description, we reproduce the characterized band structures with spontaneous exciton formation, where the interlayer inter-band coupling in TiSe2 plays a key role, which leads to an odd-to-even-layer switch of the excitonic state formation. Our results provide direct evidences of the spontaneous exciton formation, promising an excitonic condensate as versatile platform for realizing Bose-Einstein condensate (BEC) and investigating novel correlated phenomena.
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BibTeX
@misc{wang2026oddtoevenlayer,
title = {{Odd-to-Even-Layer Switch of Spontaneous Excitonic State in $\rmTiSe_2$ Thin Films}},
author = {Kaili Wang and Zhuowei Liu and Yuyang Mu and Zhujuan Li and Zhenjie Fan and Yu Gui and Xiaodong Qiu and Baigeng Wang and Rui Wang and Yi Zhang and Qi-Kun Xue},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19370},
eprint = {2610.19370},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19370},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Odd-to-Even-Layer Switch of Spontaneous Excitonic State in TiSe_2 Thin Films
AU - Kaili Wang
AU - Zhuowei Liu
AU - Yuyang Mu
AU - Zhujuan Li
AU - Zhenjie Fan
AU - Yu Gui
AU - Xiaodong Qiu
AU - Baigeng Wang
AU - Rui Wang
AU - Yi Zhang
AU - Qi-Kun Xue
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.19370
UR - https://arxiv.org/abs/2610.19370
AB - TiSe_2 is a candidate of high temperature excitonic condensates with spontaneous exciton formation in addition to its charge density wave (CDW). However, direct observation and manipulation of this electron-hole paring state formation is still lacking. Here, using varying-temperature angle-resolved photoemission spectroscopy (VT-ARPES), we observe a distinct odd-to-even-layer switch of spontaneous exciton state formation with the evident correlated band structure in TiSe_2 thin films. While the odd-layer TiSe_2 films show a sharp band structure in single-particle picture superimposed by CDW renormalization, in the even-layer TiSe_2 films, the full-filling valence band (VB) opens a distinct notch at the top, and the conductive band (CB) shows a significant extra signal extending above Fermi level with spectra broadening. These features indicate that the extra holes (notched VB) and electrons (broadening CB above Fermi level) form spontaneous excitons in even-layer TiSe_2. Based on a correlated electron-hole model extracted from the tight-binding description, we reproduce the characterized band structures with spontaneous exciton formation, where the interlayer inter-band coupling in TiSe_2 plays a key role, which leads to an odd-to-even-layer switch of the excitonic state formation. Our results provide direct evidences of the spontaneous exciton formation, promising an excitonic condensate as versatile platform for realizing Bose-Einstein condensate (BEC) and investigating novel correlated phenomena.
ER -