本文研究了非中心对称磁性Weyl半金属PrAlGe中存在较大的非线性光学ME响应，其中极性结构不对称和铁磁有序破坏了P和T对称。研究人员观察到顺磁相中P对称破缺引起的巨大二次谐波产生(SHG)，与Weyl半金属TaAs中报道的最大二次谐波响应相当。在铁磁有序相中，由于P对称性破缺和T对称性破缺而产生的非磁性SHG和磁致SHG之间的干涉导致了SHG强度的磁场切换。此外，这种干涉效应严重依赖于光的传播方向。相应的磁致非线性磁化率明显大于原型ME材料，表明存在强的非线性动力学ME耦合。本研究结果建立了P-对称和t -对称破缺ME拓扑半金属的独特光学功能性。
据悉，由反演(P)或时间反演(T)对称破缺所产生的Weyl半金属，由于Weyl节点对强Berry曲率而表现出破纪录的大光学响应。具有P和T对称破缺的不同类别的Weyl半金属可能展现出独特的光磁电（ME）响应，这与传统Weyl半金属中观察到的光学响应存在本质差异。这种ME响应赋予光传播方向依赖性和回旋效应等多功能特性。然而，迄今为止，这种（半）金属体系中的光学ME现象仍难以捉摸，尚待深入研究。
附：英文原文
Title: Large nonlinear optical magnetoelectric response in a noncentrosymmetric magnetic Weyl semimetal
Author: Shoriki, Kentaro, Moriishi, Keigo, Okamura, Yoshihiro, Yokoi, Kohei, Usui, Hidetomo, Murakawa, Hiroshi, Sakai, Hideaki, Hanasaki, Noriaki, Tokura, Yoshinori, Takahashi, Youtarou
Issue&Volume: 2024-3-14
Abstract: Weyl semimetals resulting from either inversion (P) or time-reversal (T) symmetry breaking have been revealed to show the record-breaking large optical response due to intense Berry curvature of Weyl-node pairs. Different classes of Weyl semimetals with both P and T symmetry breaking potentially exhibit optical magnetoelectric (ME) responses, which are essentially distinct from the previously observed optical responses in conventional Weyl semimetals, leading to the versatile functions such as directional dependence for light propagation and gyrotropic effects. However, such optical ME phenomena of (semi)metallic systems have remained elusive so far. Here, we show the large nonlinear optical ME response in noncentrosymmetric magnetic Weyl semimetal PrAlGe, in which the polar structural asymmetry and ferromagnetic ordering break P and T symmetry. We observe the giant second harmonic generation (SHG) arising from the P symmetry breaking in the paramagnetic phase, being comparable to the largest SHG response reported in Weyl semimetal TaAs. In the ferromagnetically ordered phase, it is found that interference between this nonmagnetic SHG and the magnetically induced SHG emerging due to both P and T symmetry breaking results in the magnetic field switching of SHG intensity. Furthermore, such an interference effect critically depends on the light-propagating direction. The corresponding magnetically induced nonlinear susceptibility is significantly larger than the prototypical ME material, manifesting the existence of the strong nonlinear dynamical ME coupling. The present findings establish the unique optical functionality of P- and T-symmetry broken ME topological semimetals.
DOI: 10.1073/pnas.2316910121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2316910121