AI 中文总结
本研究以双层石墨烯/hBN莫尔体系为对象，揭示弱磁场可通过诱导半经典轨道网络演化、产生谷选择性效应等重组莫尔电子态，为相关体系的磁场调控提供了统一物理图景。
AI 中文摘要
磁场被广泛用于通过量子振荡或调控自旋与谷极化来诊断二维体系中的量子相，但磁场也能重塑基础电子结构。本文利用双层石墨烯/hBN莫尔体系，揭示了磁场诱导的半经典轨道网络的丰富演化，包括 Lifshitz 转变、磁击穿以及共存电子和空穴口袋间的散射。在1 T至2 T的磁场下，宽载流子密度范围内的量子振荡频率和霍尔密度发生显著变化，表明存在磁击穿和磁 Lifshitz 转变。这种演化具有谷依赖性：击穿结附近的贝里曲率热点增强K谷的磁击穿，同时抑制K'谷的磁击穿；而谷反对称的轨道磁矩会分裂对应的Lifshitz转变。在更高磁场下，由此产生的谷选择性轨迹表现为谷对称破缺的 Hofstadter 能隙。在高温低磁场下，共存电子和空穴口袋间的散射会产生几乎与密度无关的电阻振荡，其频率跟踪费米面面积之和，且在常规Onsager振荡因热效应消失后仍持续存在。本研究结果为弱磁场如何在体系从半经典输运向Hofstadter区演化时重组莫尔电子态提供了统一图景。
英文摘要
Magnetic fields are widely used to diagnose quantum phases in two-dimensional systems through quantum oscillations or by tuning spin and valley polarizations, but magnetic fields can also reshape the underlying electronic structure. Here, using a bilayer graphene/hBN moiré system, we reveal a rich magnetic field induced evolution of the semiclassical orbit network, encompassing Lifshitz transitions, magnetic breakdown, and scattering between coexisting electron and hole pockets. At magnetic fields of 1 T to 2 T, quantum oscillation frequencies and the Hall density change markedly over a broad carrier density range, signaling magnetic breakdown and magnetic Lifshitz transitions. This evolution is valley contrasting: Berry curvature hot spots near the breakdown junctions enhance magnetic breakdown in the K valley while suppressing it in the K$^\prime$ valley, whereas valley-antisymmetric orbital magnetic moments split the corresponding Lifshitz transitions. The resulting valley-selective trajectories manifest at higher fields as valley-symmetry-breaking Hofstadter gaps. At elevated temperatures and low magnetic fields, scattering between coexisting electron and hole pockets produces nearly density-independent resistance oscillations whose frequency tracks the sum of their Fermi surface areas, persisting after conventional Onsager oscillations are thermally washed out. Our results provide a unified picture of how modest magnetic fields reorganize moiré electronic states as the system evolves from semiclassical transport toward the Hofstadter regime.
