Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2
Abstract
The mechanism driving the charge density wave (CDW) transition in TiSe2 has been debated for decades, with proposals ranging from an excitonic insulator to a lattice-driven instability. A central question remains whether the transition involves an opening or enhancement of the bulk band gap. Using high-resolution angle-resolved photoemission spectroscopy, we directly track the temperature evolution of the bulk band edges across the CDW transition at TCDW = 200 K. Contrary to the expectation of a gap-opening transition, we find that the size of the fundamental band gap remains constant from the high-temperature normal phase down to 160 K. While the CDW induces clear band-folding signatures and spectral weight redistribution, the underlying band extrema are unperturbed. These results demonstrate that TiSe2 does not undergo a temperature-driven electronic gap opening. Instead, they support a scenario where the transition is governed by a lattice symmetry-breaking reconstruction that folds, but does not gap, the electronic structure of a pre-existing band insulator.
Versions
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BibTeX
@misc{yilmaz2026direct,
title = {{Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2}},
author = {Turgut Yilmaz and Anil Rajapitamahuni and Muhammad Awais Fiaz and Zhenxian Liu and Jerzy T. Sadowski and Abdullah Al-Mahboob and Asish K. Kundu and Shawna M. Hollen and Boris Sinkovic and Elio Vescovo},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.05059},
eprint = {2608.05059},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.05059},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2
AU - Turgut Yilmaz
AU - Anil Rajapitamahuni
AU - Muhammad Awais Fiaz
AU - Zhenxian Liu
AU - Jerzy T. Sadowski
AU - Abdullah Al-Mahboob
AU - Asish K. Kundu
AU - Shawna M. Hollen
AU - Boris Sinkovic
AU - Elio Vescovo
PY - 2026
DA - 2026/08/05
PB - arXiv
DO - 10.48550/arxiv.2608.05059
UR - https://arxiv.org/abs/2608.05059
AB - The mechanism driving the charge density wave (CDW) transition in TiSe2 has been debated for decades, with proposals ranging from an excitonic insulator to a lattice-driven instability. A central question remains whether the transition involves an opening or enhancement of the bulk band gap. Using high-resolution angle-resolved photoemission spectroscopy, we directly track the temperature evolution of the bulk band edges across the CDW transition at TCDW = 200 K. Contrary to the expectation of a gap-opening transition, we find that the size of the fundamental band gap remains constant from the high-temperature normal phase down to 160 K. While the CDW induces clear band-folding signatures and spectral weight redistribution, the underlying band extrema are unperturbed. These results demonstrate that TiSe2 does not undergo a temperature-driven electronic gap opening. Instead, they support a scenario where the transition is governed by a lattice symmetry-breaking reconstruction that folds, but does not gap, the electronic structure of a pre-existing band insulator.
ER -