铁轴系统中的空间色散二次谐波产生
Spatially Dispersive Second-Harmonic Generation in Ferroaxial Systems
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中文总结 AI 辅助
研究铁轴系统中空间色散二次谐波产生，通过发展规范一致微观理论，应用于最小三角形团簇模型，证明EQ和MD过程对定量描述该现象必不可少，为解释中心对称多极序非线性光学特征提供微观基础。
中文摘要 AI 辅助
空间色散二次谐波产生（SHG）为超越电偶极近似的中心对称多极态提供了有力探测手段。我们发展了一种规范一致的空间色散SHG微观理论，平等对待电四极（EQ）和磁偶极（MD）过程。将该公式应用于与电环形偶极密切相关的具有铁轴序的最小三角形团簇模型，表明非线性光学响应直接反映铁轴序参量。长度规范和速度规范计算结果的一致性证实了公式的规范一致性。我们进一步证明，尽管EQ和MD贡献具有相同的共振能量，但它们表现出不同的光谱权重。特别是，在选定的共振处，MD通道可以主导EQ通道，这表明它不仅仅是微扰修正。我们的结果表明，EQ和MD过程对于定量描述铁轴材料中的空间色散SHG都是必不可少的，并为解释中心对称多极序的非线性光学特征提供了微观基础。
英文摘要
Spatially dispersive second-harmonic generation (SHG) provides a powerful probe of centrosymmetric multipolar states beyond the electric-dipole approximation. We develop a gauge-consistent microscopic theory of spatially dispersive SHG that treats electric-quadrupole (EQ) and magnetic-dipole (MD) processes on equal footing. Applying the formulation to a minimal triangular cluster model with ferroaxial order, which is closely related to an electric toroidal dipole, we show that the nonlinear optical response directly reflects the ferroaxial order parameter. The agreement between length- and velocity-gauge calculations confirms the gauge consistency of the formulation. We further demonstrate that the EQ and MD contributions exhibit different spectral weights despite sharing the same resonance energies. In particular, the MD channel can dominate over the EQ channel at selected resonances, indicating that it is not merely a perturbative correction. Our results establish that both EQ and MD processes are essential for a quantitative description of spatially dispersive SHG in ferroaxial materials and provide a microscopic basis for interpreting nonlinear optical signatures of centrosymmetric multipolar order.
