AI 中文总结
该研究针对多轨道平带体系，建立平带拉曼散射微扰理论，揭示虚拟带间过程产生由量子几何张量调控的带隙下拉曼顶点，其框架与全多轨道计算结果定量吻合，证实偏振分辨拉曼光谱可探测关联平带的集体激发。
AI 中文摘要
平带材料蕴含丰富的集体现象，但目前仍缺乏其在非弹性光散射中特征的完整理论。尽管平带相互作用的朴素理论会预测，在色散消失的极限下拉曼散射顶点完全消失，但我们证明，当考虑此类体系的多轨道特性时，该图像并不完整。我们表明，即使在严格的平带极限下，虚拟带间过程也会产生由量子几何张量调控的有限带隙下拉曼顶点。针对光子能量远偏离带间跃迁共振的极限情况，我们建立了平带拉曼散射的系统微扰理论。在同等处理带间库仑散射与光-物质耦合的前提下，我们将拉曼散射顶点分解为直接用量子几何张量表示的与相互作用无关的几何项，以及由虚拟带间库仑散射产生的有效共振和非共振部分。随后，我们研究了具有非平凡量子几何的相互作用平带的集体激发的偏振分辨拉曼响应，并证明我们的框架在光子与带间跃迁大失谐时与全多轨道计算结果定量吻合。这些结果确立了量子几何是平带体系中非弹性光散射的本征贡献，并表明偏振分辨拉曼光谱可作为量子几何敏感探针，用于探测关联平带平台的集体激发。
英文摘要
Flat-band materials host rich collective phenomena, yet a complete theory of their signatures in inelastic light scattering remains lacking. While naive theories of interacting flat bands would predict that Raman scattering vertices vanish identically in the limit of vanishing dispersion, we show that this picture is incomplete upon including the multiorbital character of such systems. We show that virtual interband processes generate a finite subgap Raman vertex controlled by the quantum geometric tensor even in the strict flat-band limit. We develop a systematic perturbative theory for Raman scattering from flat bands in the limit where the photon energy is far from resonance with interband transitions. Treating interband Coulomb scattering and light-matter coupling on equal footing, we decompose the Raman scattering vertices into an interaction-independent geometric term expressible directly in terms of the quantum geometric tensor, together with effective resonant and non-resonant pieces generated by virtual interband Coulomb scattering. We then study the polarization-resolved Raman response from collective excitations of an interacting flat band with nontrivial quantum geometry, and demonstrate quantitative agreement of our framework with a full multi-orbital calculation at large photon detuning from interband transitions. These results establish quantum geometry as an intrinsic contribution to inelastic light scattering in flat-band systems, and suggest polarization-resolved Raman spectroscopy as a quantum geometry-sensitive probe of the collective excitations of correlated flat-band platforms.
Comments18 pages, 6 figures
