Infrared evidence for strong C3 symmetry breaking in 1T-TiSe2
Abstract
The interplay between lattice and electron degrees of freedom gives rise to competing ordered states in quantum materials, which can lead to a series of subsequent symmetry breaking transitions. While the differences are often subtle, these phases can be distinguished by their remaining point group symmetries. Here, we use infrared optical spectroscopy to probe symmetry breaking at the charge density wave transition of 1T-TiSe2. We uncover a previously unobserved splitting of a doubly degenerate Eu optical phonon at TCDW≈ 190 K that constitutes direct evidence for the breaking of three-fold rotational symmetry. Our finding rules out proposals where the CDW transition to a low temperature chiral or nematic phase takes place through an intermediary state that preserves three-fold symmetry. The energy difference between the two former Eu partners can only be explained by large C3 breaking distortions of the same order of magnitude as previously observed changes in bond lengths, suggesting that C3 symmetry breaking plays a dominant role in the CDW transition. The linewidth of the single phonon mode above TCDW could be consistent with a fluctuating state where three-fold symmetry is also broken.
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BibTeX
@misc{grondelle2026infrared,
title = {{Infrared evidence for strong $C_3$ symmetry breaking in 1$T$-TiSe$_2$}},
author = {Esther van Grondelle and Kai Rossnagel and Jasper van Wezel and Erik van Heumen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.24705},
eprint = {2609.24705},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.24705},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Infrared evidence for strong C_3 symmetry breaking in 1T-TiSe_2
AU - Esther van Grondelle
AU - Kai Rossnagel
AU - Jasper van Wezel
AU - Erik van Heumen
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.24705
UR - https://arxiv.org/abs/2609.24705
AB - The interplay between lattice and electron degrees of freedom gives rise to competing ordered states in quantum materials, which can lead to a series of subsequent symmetry breaking transitions. While the differences are often subtle, these phases can be distinguished by their remaining point group symmetries. Here, we use infrared optical spectroscopy to probe symmetry breaking at the charge density wave transition of 1T-TiSe_2. We uncover a previously unobserved splitting of a doubly degenerate E_u optical phonon at T_CDW≈ 190 K that constitutes direct evidence for the breaking of three-fold rotational symmetry. Our finding rules out proposals where the CDW transition to a low temperature chiral or nematic phase takes place through an intermediary state that preserves three-fold symmetry. The energy difference between the two former E_u partners can only be explained by large C_3 breaking distortions of the same order of magnitude as previously observed changes in bond lengths, suggesting that C_3 symmetry breaking plays a dominant role in the CDW transition. The linewidth of the single phonon mode above T_CDW could be consistent with a fluctuating state where three-fold symmetry is also broken.
ER -