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arXiv · 2608.05059

Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2

Turgut Yilmaz·Anil Rajapitamahuni·Muhammad Awais Fiaz·Zhenxian Liu·Jerzy T. Sadowski·Abdullah Al-Mahboob·Asish K. Kundu·Shawna M. Hollen·Boris Sinkovic·Elio Vescovo
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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.

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Turgut Yilmaz, Anil Rajapitamahuni, Muhammad Awais Fiaz, Zhenxian Liu, Jerzy T. Sadowski, Abdullah Al-Mahboob, Asish K. Kundu, Shawna M. Hollen, Boris Sinkovic, Elio Vescovo. 2026-08-05. Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2. https://doi.org/10.1103/z2j1-gwj4

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