Department of Chemistry, University of California, Berkeley, California 94720, United States.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Nano Lett. 2021 Jul 28;21(14):6095-6101. doi: 10.1021/acs.nanolett.1c01502. Epub 2021 Jul 15.
The coexistence of ferroelectricity and metallicity seems paradoxical, since the itinerant electrons in metals should screen the long-range dipole interactions necessary for dipole ordering. The recent discovery of the polar metal LiOsO was therefore surprising [as discussed earlier in Y. Shi et al., . , , 1024]. It is thought that the coordination preferences of the Li play a key role in stabilizing the LiOsO polar metal phase, but an investigation from the combined viewpoints of core-state specificity and symmetry has yet to be done. Here, we apply the novel technique of extreme ultraviolet second harmonic generation (XUV-SHG) and find a sensitivity to the broken inversion symmetry in the polar metal phase of LiOsO with an enhanced feature above the Li K-edge that reflects the degree of Li atom displacement as corroborated by density functional theory calculations. These results pave the way for time-resolved probing of symmetry-breaking structural phase transitions on femtosecond time scales with element specificity.
铁电性和金属性共存似乎自相矛盾，因为金属中的巡游电子应该屏蔽长程偶极子相互作用所必需的长程偶极子相互作用。因此，最近发现的极性金属 LiOsO 令人惊讶[正如 Y. Shi 等人之前讨论的那样，。。。，1024]。人们认为 Li 的配位偏好在稳定 LiOsO 极性金属相方面起着关键作用，但尚未从核心态特异性和对称性的综合观点进行研究。在这里，我们应用新型的极紫外二次谐波产生 (XUV-SHG) 技术，发现 LiOsO 极性金属相中存在对破缺反演对称性的敏感性，在 Li K 边缘上方增强了特征，这反映了 Li 原子位移的程度，正如密度泛函理论计算所证实的那样。这些结果为在飞秒时间尺度上对具有元素特异性的对称破缺结构相变进行时间分辨探测铺平了道路。
