Jog Harshvardhan, Harnagea Luminita, Mele Eugene J, Agarwal Ritesh
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
Department of Physics, Indian Institute of Science Education and Research, Pune, Maharashtra 411008, India.
Sci Adv. 2022 Feb 18;8(7):eabl9020. doi: 10.1126/sciadv.abl9020. Epub 2022 Feb 16.
In low-electron density materials, interactions can lead to highly correlated quantum states of matter. TaNiSe, an excitonic insulator (EI) candidate, exists in a novel broken-symmetry phase below 327 K, characterized by robust exchange interaction and electron-lattice coupling. We study this phase of TaNiSe using the quadrupole circular photogalvanic effect (QCPGE). Light-matter interaction in TaNiSe mediated by electric quadrupole/magnetic dipole coupling produces helicity-dependent DC response even with centrosymmetry, making it particularly sensitive to certain other broken symmetries. We show that the exchange interaction in TaNiSe can lead to a triclinic structure with a broken symmetry. Our results provide an incisive probe of the symmetries of the low-temperature phase of TaNiSe and add new symmetry constraints to the identification of a strongly correlated EI phase. The high sensitivity of QCPGE to subtle symmetry breaking in centrosymmetric systems will enable its use in studying other complex crystalline systems.
在低电子密度材料中，相互作用可导致高度相关的量子物质状态。TaNiSe作为一种激子绝缘体（EI）候选材料，在327 K以下存在于一种新型的破缺对称相中，其特征是具有强大的交换相互作用和电子-晶格耦合。我们使用四极圆光电流效应（QCPGE）研究TaNiSe的这一相。即使在具有中心对称性的情况下，由电四极/磁偶极耦合介导的TaNiSe中的光-物质相互作用也会产生与螺旋度相关的直流响应，这使得它对某些其他破缺对称性特别敏感。我们表明，TaNiSe中的交换相互作用可导致具有破缺对称性的三斜结构。我们的结果为TaNiSe低温相的对称性提供了敏锐的探测，并为识别强关联EI相增加了新的对称性约束。QCPGE对中心对称系统中细微对称性破缺的高灵敏度将使其能够用于研究其他复杂晶体系统。
