美国SLAC国家加速器实验室Mariano Trigo团队研究了SrTiO₃中极化密度波的观测。相关论文发表在2025年4月7日出版的《自然—物理学》杂志上。

SrTiO₃中初始铁电转变的性质一直是凝聚态物理学中的一个长期难题。一种解释涉及铁电性和以介观极化调制为特征的不稳定性之间的竞争。这些极化密度波在量子临界点附近会增强，破坏了局部反演对称性，很难用传统的X射线散射方法进行表征。

研究组通过将飞秒X射线自由电子激光与太赫兹相干控制方法相结合，在有限动量下探测反转对称性破缺，并在纳米尺度上可视化SrTiO₃中极化的不稳定性。他们发现极性声学集体模式是柔软的，特别是在几十纳米尺度上。这些前驱体集体激发为SrTiO₃中推测的介观调制相提供了证据。

附：英文原文

Title: Observation of polarization density waves in SrTiO3

Author: Orenstein, Gal, Krapivin, Viktor, Huang, Yijing, Zhang, Zhuquan, de la Pea Muoz, Gilberto, Duncan, Ryan A., Nguyen, Quynh, Stanton, Jade, Teitelbaum, Samuel, Yavas, Hasan, Sato, Takahiro, Hoffmann, Matthias C., Kramer, Patrick, Zhang, Jiahao, Cavalleri, Andrea, Comin, Riccardo, Dean, Mark P. M., Disa, Ankit S., Frst, Michael, Johnson, Steven L., Mitrano, Matteo, Rappe, Andrew M., Reis, David, Zhu, Diling, Nelson, Keith A., Trigo, Mariano

Issue&Volume: 2025-04-07

Abstract: The nature of the incipient ferroelectric transition in SrTiO3 has been a long-standing puzzle in condensed matter physics. One explanation involves the competition between ferroelectricity and an instability characterized by the mesoscopic modulation of the polarization. These polarization density waves, which should intensify near the quantum critical point, break local inversion symmetry and are difficult to characterize with conventional X-ray scattering methods. Here we probe inversion symmetry breaking at finite momenta and visualize the instability of the polarization at the nanometre scale in SrTiO3 by combining a femtosecond X-ray free-electron laser with terahertz coherent control methods. We found polar-acoustic collective modes that are soft, particularly at the tens of nanometre scale. These precursor collective excitations provide evidence for the conjectured mesoscopic-modulated phase in SrTiO3.

DOI: 10.1038/s41567-025-02874-0

Source: https://www.nature.com/articles/s41567-025-02874-0