Two-dimensional (2D) lateral heterojunctions between different transition metal dichalcogenides (TMDCs) have been realized in recent years. Homogeneous semiconducting TMDC layers are characterized by a topological invariant, their in-plane electric polarization. It suggests the possibility of one-dimensional (1D) metallic states at heterojunctions where the value of the invariant changes. We study such lateral 2D TMDC junctions by means of first-principles calculations and show that 1D metallic states emerge even in cases where the different materials are joined epitaxially. We find that the metallicity does not depend on structural details, but, as the invariant is protected by spatial symmetry only, it can be upset by breaking the symmetry. Indeed, 1D charge- and spin-density wave instabilities appear spontaneously, making 2D TMDC heterojunctions ideal systems for studying 1D systems.

近年来，已经实现了不同过渡金属二卤化物（TMDC）之间的二维（2D）横向异质结。均匀的半导体TMDC层的特征在于拓扑不变性，即它们的面内极化。这表明在不变量值发生变化的异质结处可能存在一维（1D）金属态。我们通过第一性原理计算研究了此类横向2D TMDC结，并表明即使在不同材料外延连接的情况下，一维金属态也会出现。我们发现，金属性不依赖于结构细节，但是，由于不变性仅受空间对称性的保护，因此可以通过破坏对称性来破坏它。实际上，一维电荷和自旋密度波的不稳定性会自发出现，