Boundary-Obstructed Topological High-Tc Superconductivity in Iron Pnictides*

Nontrivial topology and unconventional pairing are two central guiding principles in the contemporary search for and analysis of superconducting materials and heterostructure compounds. It is quite rare that a single material compound possesses both non-trivial topological electronic band structure and unconventional pairing. In this work, we will describe an example of such system in iron-based superconductors. We propose to realize high-order topological superconductors, a new topological phase with the gapless modes located at the corner/hinge instead of the edge/surface, in the 112-family of iron pnictides, such as Ca_1-xLa_xFeAs₂ [1], with the great advantage of the Curie temperature above 40K. Our theory provides the microscopic physical mechanism and topological characterization of this topological phase. Our works not only provide a physical understanding of the existing experiments, but also opens a new arena for high-order topological superconductivity with stable corner/hinge Majorana modes in intrinsic superconductors with high Curie temperature.