Excitonic insulators are insulating states formed by the coherent condensation of electron and hole pairs into BCS-like states. Isotropic spatial wave functions are commonly considered for excitonic condensates since the attractive interaction among the electrons and the holes in semiconductors usually leads to s-wave excitons. Here, we propose a new type of excitonic insulator that exhibits order parameter with p + ip symmetry and is characterized by a chiral Chern number C_c = 1/2. This state displays the parity anomaly, which results in two novel topological properties: fractionalized excitations with e/2 charge at defects and a spontaneous in-plane magnetization. The topological insulator surface state is a promising platform to realize the topological excitonic insulator. With the spin-momentum locking, the interband optical pumping can renormalize the surface electrons and drive the system towards the proposed p + ip instability.

中文翻译：

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具有奇偶校验异常的拓扑p + ip激子绝缘体的预测。

激子绝缘体是通过电子和空穴对的相干凝聚成BCS样态而形成的绝缘态。对于激子冷凝物，通常考虑各向同性的空间波函数，因为电子与半导体中的空穴之间的吸引相互作用通常会导致s波激子。在这里，我们提出了一种新型的激子绝缘子，它表现出具有p + ip对称性的阶数参数，并且具有手性Chern数C _{c的特征。} = 1/2。此状态显示奇偶校验异常，从而导致两个新的拓扑特性：缺陷处具有e / 2电荷的分段激发和自发平面磁化。拓扑绝缘子的表面状态是实现拓扑激子绝缘子的有前途的平台。通过自旋动量锁定，带间光泵浦可以使表面电子重新规范化，并使系统趋向于所提出的p + ip不稳定性。