Esparza Juan Pablo, Juričić Vladimir
Universidad Técnica Federico Santa María, Departamento de Física, Casilla 110, Valparaíso, Chile.
Pontificia Universidad Católica de Valparaíso, Instituto de Física, Avenida Universidad 331, Curauma, Valparaíso, Chile.
Phys Rev Lett. 2025 Jun 6;134(22):226602. doi: 10.1103/dl59-vl7v.
Twisted bilayer graphene (TBG) features strongly correlated and topological phases due to its flat bands emerging near the magic angle. However, the effects of the non-Hermiticity, arising from the coupling to the environment and dissipation, have remained unexplored. We here develop a simple non-Hermitian (NH) version of twisted bilayer graphene (TBG) by considering relative twisting of two NH graphene monolayers with non-Hermiticity encoded in the imbalance of in-plane nearest-neighbor hopping amplitudes. Remarkably, by generalizing the Bistritzer-MacDonald approach to NH systems, we discover exceptional magic angles where the band structure changes from purely real to purely imaginary thus featuring flat bands with infinite lifetime. Between them, the bands remain flattened, and a Hermitian magic angle emerges at which the imaginary part of energy is maximal, and corresponds to the usual magic angle in nondissipative, purely Hermitian TBG. We propose an optical lattice setup with gain and loss where our theoretical predictions can be verified. These results suggest the robustness of the flat bands in open systems, paving the way for the further studies on the interplay of dissipative effects, electronic topology, and interactions in such NH moiré bands.
扭曲双层石墨烯（TBG）由于在魔角附近出现平带而具有强关联和拓扑相。然而，由于与环境的耦合和耗散产生的非厄米性效应尚未得到探索。我们在此通过考虑两个非厄米石墨烯单层的相对扭曲来开发一种简单的非厄米（NH）版本的扭曲双层石墨烯（TBG），其中非厄米性通过面内最近邻跳跃幅度的不平衡来编码。值得注意的是，通过将Bistritzer - MacDonald方法推广到NH系统，我们发现了特殊的魔角，在这些魔角处能带结构从纯实变为纯虚，从而具有无限寿命的平带。在它们之间，能带保持平坦，并且出现一个厄米魔角，此时能量的虚部最大，并且对应于无耗散、纯厄米TBG中的通常魔角。我们提出了一种具有增益和损耗的光学晶格设置，在其中我们的理论预测可以得到验证。这些结果表明开放系统中平带的稳健性，为进一步研究此类NH莫尔带中的耗散效应、电子拓扑和相互作用之间的相互作用铺平了道路。
