We investigate the Bloch flat bands in twisted bilayers from nonpolar to polar two-dimensional semiconductors using first-principles calculations and density functional based tight-binding simulations. First, to delineate the underlying mechanism of the formation of the flat bands, we rely on a tight-binding model of modified graphene where a bias between the A-B sublattice of the hexagonal lattice is introduced. By analyzing the evolution of the valence and conduction band edges of the bilayer of the modified graphene with different stacking patterns, a mechanism attributed to the splitting of the defect-like band edge states induced by different stacking patterns is revealed. The magic angle mechanism is no longer needed. Next, guided by the revealed mechanism, we predict the formation of flat bands in twisted bilayers of a series of two-dimensional systems from nonpolar to polar semiconductors. Our finding has important implications for exploring the flat band physics in low dimensions.

中文翻译：

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极性二维半导体的扭曲双层中的平坦带

我们使用第一性原理计算和基于密度泛函的紧密结合模拟研究从非极性到极性二维半导体的双分子层中的Bloch平坦带。首先，为了描述形成平带的基本机理，我们依赖于改性石墨烯的紧密结合模型，其中引入了六角形晶格的AB子晶格之间的偏差。通过分析具有不同堆叠图案的改性石墨烯的双层的价键和导带边缘的演变，揭示了归因于由不同堆叠图案引起的缺陷状带边缘状态的分裂的机制。不再需要魔角机制。接下来，在揭示的机制的指导下，我们预测了从非极性半导体到极性半导体的一系列二维系统的扭曲双层中平坦带的形成。我们的发现对探索低维度的扁平带物理具有重要意义。