Revealing Hidden Inversion Symmetry Breaking in ZrTe5 via Phonon-Assisted Heterodyne Amplification
Abstract
ZrTe5 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 ZrTe5 and establish a structural constraint for understanding its electronic and topological properties.
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BibTeX
@misc{li2026revealing,
title = {{Revealing Hidden Inversion Symmetry Breaking in ZrTe$_5$ via Phonon-Assisted Heterodyne Amplification}},
author = {S. J. Li and J. H. Huang and H. Y. Wu and S. P. Zheng and C. J. Kong and B. Xu and H. Wang and T. Dong and L. Yue and D. Wu and Y. Wan and Z. L. Li and X. B. Wang and S. J. Zhang and N. L. Wang and Y. T. Li},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.12359},
eprint = {2609.12359},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.12359},
}
RIS
TY - UNPB
TI - Revealing Hidden Inversion Symmetry Breaking in ZrTe_5 via Phonon-Assisted Heterodyne Amplification
AU - S. J. Li
AU - J. H. Huang
AU - H. Y. Wu
AU - S. P. Zheng
AU - C. J. Kong
AU - B. Xu
AU - H. Wang
AU - T. Dong
AU - L. Yue
AU - D. Wu
AU - Y. Wan
AU - Z. L. Li
AU - X. B. Wang
AU - S. J. Zhang
AU - N. L. Wang
AU - Y. T. Li
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2609.12359
UR - https://arxiv.org/abs/2609.12359
AB - 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.
ER -