发表机构
University of Amsterdam; Deutsches Elektronen-Synchrotron DESY; Christian-Albrechts-Universität zu Kiel（阿姆斯特丹大学; 德国电子同步加速器中心; 基尔大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过红外光谱发现1T-TiSe2中E_u声子在CDW转变处分裂，直接证明C3对称性破缺，排除中间态保持三次对称的模型，表明C3破缺在转变中起主导作用。
AI 中文摘要
晶格与电子自由度之间的相互作用在量子材料中引发了相互竞争的有序态，这可能导致一系列后续的对称性破缺转变。尽管这些差异往往很微妙，但这些相可以通过它们剩余的点群对称性来区分。在这里，我们使用红外光谱学来探测1$T$-TiSe$_{2}$电荷密度波转变处的对称性破缺。我们发现了在$T_{\mathrm{CDW}}\approx$ 190 K处一个双重简并的$E_u$光学声子先前未被观察到的分裂，这构成了三次旋转对称性破缺的直接证据。我们的发现排除了那些提出CDW转变通过一个保持三次对称性的中间态进入低温手性或向列相的提议。两个前$E_{u}$伙伴之间的能量差只能通过与先前观察到的键长变化同数量级的大$C_{3}$破缺畸变来解释，这表明$C_{3}$对称性破缺在CDW转变中起着主导作用。在$T_{\mathrm{CDW}}$以上单一声子模式的线宽可能与一个三次对称性也被破缺的涨落态一致。
英文摘要
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 1$T$-TiSe$_{2}$. We uncover a previously unobserved splitting of a doubly degenerate $E_u$ optical phonon at $T_{\mathrm{CDW}}\approx$ 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 $T_{\mathrm{CDW}}$ could be consistent with a fluctuating state where three-fold symmetry is also broken.
Comments6 pages, 3 figures, 2 appendices with 2 figures
