AI 中文总结
研究利用舒布尼科夫-德哈斯光谱对四层石墨烯器件进行实验，定量重构六种费米面拓扑，提取振荡频率确定相关参数，还发现磁场与位移场结合可解除能谷简并，为追踪多带量子材料费米面拓扑及简并度提供框架。
AI 中文摘要
量子振荡可直接探测费米面拓扑和电子简并度，但在多带系统的里夫希茨跃迁中同时解析两者仍是实验挑战。本文利用舒布尼科夫-德哈斯光谱，对高迁移率、双栅伯纳尔堆叠四层石墨烯（B-4LG）器件进行定量重构，得到六种不同费米面拓扑序列。提取的振荡频率确定了极值动量空间面积及其自旋、能谷和沟壑分辨的简并度，与紧束缚计算定量一致。还表明垂直磁场与位移场结合通过轨道塞曼耦合解除能谷简并，产生数meV的单粒子能谷分裂。该工作为追踪多带量子材料中费米面拓扑及其味简并度提供框架。
英文摘要
Quantum oscillations offer a direct probe of Fermi-surface topology and electronic degeneracy, yet disentangling both simultaneously across the Lifshitz transitions of multiband systems has remained an open experimental challenge. Here, we use Shubnikov-de Haas spectroscopy on a high-mobility, dual-gated Bernal-stacked tetralayer graphene (B-4LG) device to quantitatively reconstruct the complete sequence of six distinct Fermi-surface topologies-gully, annular, singly connected, and multiband pockets. The extracted oscillation frequencies determine the extremal momentum-space areas and their spin, valley, and gully-resolved degeneracies, in quantitative agreement with our tight-binding calculations. We further show that a perpendicular magnetic-field, combined with displacement-field lifts the valley degeneracy through an orbital-Zeeman coupling, producing a single-particle valley splitting of several $meV$, far larger than in bilayer or trilayer graphene. Our work demonstrates a framework for tracking Fermi-surface topologies and their flavor degeneracies in multiband quantum materials.
