发表机构
Universidad Nacional Autónoma de México (UNAM); NYU Shanghai; NYU-ECNU Institute of Physics at NYU Shanghai; Hainan University; IMDEA Nanoscience; Donostia International Physics Center（墨西哥国立自治大学; 纽约大学上海分校; 纽约大学上海纽约大学物理研究所; 海南大学; IMDEA纳米科学研究所; 圣塞巴斯蒂安国际物理中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文通过平方哈密顿量方法研究超越手性极限的双层转角石墨烯，发现晶格弛豫使约束势近均匀且隧穿比接近特殊点，解释了第一个魔角稳健而高阶魔角失稳的机制。
AI 中文摘要
我们发展了超越手性极限的双层转角石墨烯的哈密顿量平方描述，以解释为什么第一个魔角在晶格弛豫下保持稳健，而高阶魔角则被强烈地不稳定化。从具有有限同亚晶格隧穿的非手性Bistritzer--MacDonald模型出发，我们表明晶格弛豫重塑了有效约束景观，而非仅作为手性理论的简单微扰。一个核心结果是，现实的弛豫重正化隧穿比接近一个特殊的约束点，在该点对称约束势的振荡部分几乎抵消。这使得现实的双层转角石墨烯处于近乎均匀的约束区域。同时，有限的同亚晶格隧穿激活了一个额外的亚晶格间类电流通道，该通道与手性轨道通道竞争。第一个魔角之所以幸存，是因为这些约束和类电流贡献保持平衡，而高阶魔角则因更强的远程带杂化和在AA区域周围增强的实空间局域化而失去这种平衡。我们的结果为手性魔角层级结构的破坏提供了单粒子机制，并阐明了为什么实验相关的第一个魔角仍然是手性平带结构最稳定的残余。
英文摘要
We develop a squared-Hamiltonian description of twisted bilayer graphene beyond the chiral limit to explain why the first magic angle remains robust under lattice relaxation, while higher-order magic angles are strongly destabilized. Starting from the non-chiral Bistritzer--MacDonald model with finite same-sublattice tunneling, we show that lattice relaxation reshapes the effective confinement landscape rather than acting as a simple perturbation of the chiral theory. A central result is that the realistic relaxation-renormalized tunneling ratio lies close to a special confinement point where the oscillatory part of the symmetric confinement potential nearly cancels. This places realistic twisted bilayer graphene near a nearly uniform confinement regime. At the same time, finite same-sublattice tunneling activates an additional inter-sublattice current-like channel that competes with the chiral orbital channel. The first magic angle survives because these confinement and current-like contributions remain balanced, whereas higher-order magic angles lose this balance through stronger remote-band hybridization and enhanced real-space localization around AA regions. Our results provide a single-particle mechanism for the breakdown of the chiral magic-angle hierarchy and clarify why the experimentally relevant first magic angle remains the most stable remnant of the chiral flat-band structure.
Comments21 pages and 13 figures
