利用康普顿散射揭示隐藏的磁电多极子
Revealing hidden magneto-electric multipoles using Compton scattering
摘要：
磁电多极子在空间反演$\cal I$和时间反演$\cal T$对称性下都是奇数，是理解和表征磁电材料的基础。然而，这些磁电多极子的检测通常不是直接的，因为它们在常规实验中部分地保持“隐藏”，因为许多磁电体表现出组合的$\cal IT$对称性。在目前的工作中，我们表明，反对称康普顿轮廓是一个独特的签名，所有的磁电多极子，因为不对称的磁化强度密度耦合到空间通过自旋轨道耦合，导致反对称康普顿轮廓。我们开发的反对称康普顿散射的对称性分析的关键物理，并证明它使用明确的第一性原理计算两个著名的代表性材料的磁电多极，绝缘LiNiPO $_4$和金属Mn $_2$ Au。我们的工作强调了自旋矩的取向、自旋轨道耦合和能带结构在磁电材料中产生反对称康普顿轮廓中的关键作用。
英文摘要：
Magneto-electric multipoles, which are odd under both space-inversion $\cal I$ and time-reversal $\cal T$ symmetries, are fundamental in understanding and characterizing magneto-electric materials. However, the detection of these magneto-electric multipoles is often not straightforward as they remain "hidden" in conventional experiments in part since many magneto-electrics exhibit combined $\cal IT$ symmetry. In the present work, we show that the anti-symmetric Compton profile is a unique signature for all the magneto-electric multipoles, since the asymmetric magnetization density of the magneto-electric multipoles couples to space via spin-orbit coupling, resulting in an anti-symmetric Compton profile. We develop the key physics of the anti-symmetric Compton scattering using symmetry analysis and demonstrate it using explicit first-principles calculations for two well-known representative materials with magneto-electric multipoles, insulating LiNiPO$_4$ and metallic Mn$_2$Au. Our work emphasizes the crucial roles of the orientation of the spin moments, the spin-orbit coupling, and the band structure in generating the anti-symmetric Compton profile in magneto-electric materials.
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