通过声子辅助外差放大揭示ZrTe$_5$中隐藏的反演对称性破缺
Revealing Hidden Inversion Symmetry Breaking in ZrTe$_5$ via Phonon-Assisted Heterodyne Amplification
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中文总结 AI 辅助
本文利用太赫兹场诱导二次谐波产生（TFISH）结合声子辅助外差放大，在块体ZrTe$_5$中直接观测到平衡态反演对称性破缺，识别出沿a轴的体极性畸变，为理解其电子和拓扑性质提供了关键结构约束。
中文摘要 AI 辅助
ZrTe$_5$是一种敏感拓扑材料，微小的扰动即可改变其电子结构。其平衡晶体结构被广泛认为具有中心对称性，而近期的实验提出了反演对称性破缺的可能性。在此，我们利用非线性光谱学探测这种隐藏的对称性降低。尽管传统的二次谐波产生无法分辨出平衡态对称性破缺信号，但太赫兹场诱导的二次谐波产生（TFISH）通过声子辅助外差放大揭示了该信号。一个相干驱动的红外活性声子充当极弱的二阶极化率$\chi^{(2)}$的本地振荡器，将原本无法检测的对称性破缺响应转换为TFISH信号的声子频率调制。该调制的场线性标度表明$\chi^{(2)}$是一种平衡态极化率，而非由太赫兹场诱导的响应。偏振和温度依赖的测量识别出沿晶体学$a$轴的体极性畸变，该畸变持续至室温，而$c$轴保持非极性。这些结果为块体ZrTe$_5$中平衡态反演对称性破缺提供了直接的光学证据，并为其电子和拓扑性质的理解建立了结构约束。
英文摘要
ZrTe$_5$ is a sensitive topological material where small perturbations can alter its electronic structure. Its equilibrium crystal structure has been widely regarded as centrosymmetric, while recent experiments have raised the possibility of inversion-symmetry breaking. Here we probe this hidden symmetry lowering using nonlinear optical spectroscopy. Although conventional second-harmonic generation does not resolve an equilibrium symmetry-breaking signal, terahertz-field-induced second-harmonic generation (TFISH) reveals it through phonon-assisted heterodyne amplification. A coherently driven infrared-active phonon acts as a local oscillator for the vanishingly weak second-order susceptibility $χ^{(2)}$, converting an otherwise undetectable symmetry-breaking response into a phonon-frequency modulation of the TFISH signal. The field-linear scaling of this modulation demonstrates $χ^{(2)}$ is an equilibrium susceptibility rather than a response induced by the THz field. Polarization- and temperature-dependent measurements identify a bulk polar distortion along the crystallographic $a$ axis that persists to room temperature, while the $c$ axis remains nonpolar. These results provide direct optical evidence for equilibrium inversion-symmetry breaking in bulk ZrTe$_5$ and establish a structural constraint for understanding its electronic and topological properties.
发表机构
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）
- School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）
- International Center for Quantum Materials, School of Physics, Peking University（北京大学物理学院量子材料中心）
- Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学汤川研究所）
- Zhangjiang Institute for Advanced Study, Shanghai Jiao Tong University（上海交通大学张江高等研究院）
机构由 AI 辅助整理，请以论文原文为准。
