阿尔特磁体中压磁诱导对称破缺的光谱指标
Spectral Indicators of Piezomagnetically Induced Symmetry Breaking in Altermagnets
AI总结：
本研究通过XMLD和XMCD揭示阿尔特磁体中压磁效应诱导的多极序，提供了一种基于对称性的方法来识别隐藏的铁电多极和可调自旋现象。
摘要：
近年来，多极重述的X射线吸收光谱（XAS）的进展为描述磁性和轨道响应提供了统一的框架，基于铁电多极序参数。X射线磁圆二色性（XMCD）已知可以探测自旋、轨道和各向异性磁偶极（AMD）矩。其在阿尔特磁体和非列线反铁磁体中的应用揭示了XMCD响应通常由激发态中的AMD铁电态而非基态中的传统磁偶极矩所支配。在本工作中，我们将基于多极的分析扩展到X射线磁线性二色性（XMLD），并证明XMLD在阿尔特磁体中可以被理解为压磁效应的体现：磁偶极矩与电四极矩之间的线性耦合。通过结合对称性分析和精确对角化计算$L_{2,3}$-边XAS，我们系统地研究了代表性的阿尔特磁体，包括$α$-MnTe、MnF$_2$和CrSb。我们证明了更高阶磁多极的铁电序，特别是带自旋的磁八极，会产生特征的场奇XMLD信号，直接反映由磁点群对称性允许的压磁响应张量。此外，我们讨论了由压磁效应诱导的XMCD信号，其中应变会生成磁偶极矩。我们的结果确立了XMLD和XMCD作为元素特异性探针，用于探测阿尔特磁体中的磁弹性多极序，并提供了一种通用的对称性基于路径，以识别隐藏的铁电多极和超越传统铁磁性的可调自旋现象。
英文摘要：
Recent developments in the multipole reformulation of X-ray absorption spectroscopy (XAS) have provided a unified framework to describe magnetic and orbital responses in terms of ferroic multipole order parameters. X-ray magnetic circular dichroism (XMCD) is known to probe spin, orbital, and anisotropic magnetic dipole (AMD) moments. Its applications to altermagnets and noncollinear antiferromagnets have revealed that the XMCD response is often governed by the ferroic states of the AMD in the photo-excited states rather than by conventional magnetic dipoles in the ground states. In this work, we extend the multipole-based analysis to X-ray magnetic linear dichroism (XMLD) and demonstrate that XMLD in altermagnets can be understood as a manifestation of piezomagnetic effects: linear couplings between magnetic dipole and electric quadrupole moments. Using symmetry analysis combined with exact diagonalization calculations of $L_{2,3}$-edge XAS, we systematically investigate representative altermagnets, including $α$-MnTe, MnF$_2$, and CrSb. We show that the ferroic ordering of higher-rank magnetic multipoles, particularly spinful magnetic octupoles, gives rise to characteristic field-odd XMLD signals that directly reflect the underlying piezomagnetic response tensors allowed by magnetic point-group symmetry. Furthermore, we discuss XMCD signals induced by piezomagnetic effects, in which strain generates magnetic dipole moments. Our results establish XMLD and XMCD as element-specific probes of magnetoelastic multipole order in altermagnets and provide a general symmetry-based pathway to identify hidden ferroic multipoles and strain-controllable spin phenomena beyond conventional ferromagnetism.
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