Xie Ming, Pan Haining, Wu Fengcheng, Das Sarma Sankar
Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Phys Rev Lett. 2023 Jul 28;131(4):046402. doi: 10.1103/PhysRevLett.131.046402.
We study the effect of interelectron Coulomb interactions on the displacement field induced topological phase transition in transition metal dichalcogenide moiré heterobilayers. We find a nematic excitonic insulator phase that breaks the moiré superlattice's threefold rotational symmetry and preempts the topological phase transition in both AA and AB stacked heterobilayers when the interlayer tunneling is weak, or when the Coulomb interaction is not strongly screened. The nematicity originates from the frustration between the nontrivial spatial structure of the interlayer tunneling, which is crucial to the existence of the topological Chern band, and the interlayer coherence induced by the Coulomb interaction that favors uniformity in layer pseudospin orientations. We construct a unified effective two-band model that captures the physics near the band inversion and applies to both AA and AB stacked heterobilayers. Within the two-band model the competition between the nematic excitonic insulator phase and the Chern insulator phase can be understood as the switching of the energetic order between the s-wave and the p-wave excitons upon increasing the interlayer tunneling.
我们研究了电子间库仑相互作用对过渡金属二硫属化物莫尔异质双层中位移场诱导的拓扑相变的影响。我们发现了一种向列激子绝缘体相，它打破了莫尔超晶格的三重旋转对称性，并且当层间隧穿较弱或库仑相互作用没有被强烈屏蔽时，在AA和AB堆叠的异质双层中都先于拓扑相变出现。这种向列性源于层间隧穿的非平凡空间结构（这对拓扑陈带的存在至关重要）与库仑相互作用诱导的层间相干性之间的相互制约，后者有利于层赝自旋取向的均匀性。我们构建了一个统一的有效双带模型，该模型捕捉了带反转附近的物理现象，并适用于AA和AB堆叠的异质双层。在双带模型中，向列激子绝缘体相和陈绝缘体相之间的竞争可以理解为随着层间隧穿增加，s波激子和p波激子之间能量顺序的切换。
