Majorana corner and hinge modes in second-order topological insulator/superconductor heterostructures

As platforms of Majorana modes, topological insulator (quantum anomalous Hall insulator)/superconductor heterostructures have attracted tremendous attention over the past decade. Here we substitute the topological insulator with its higher-order counterparts. Concretely, we consider second-order topological insulators (SOTIs) without time-reversal symmetry and investigate SOTI/superconductor heterostructures in both two and three dimensions. Remarkably, we find that such novel heterostructures provide natural realizations of second-order topological superconductors (SOTSCs) which host Majorana corner modes in two dimensions and chiral Majorana hinge modes in three dimensions. As here the realization of SOTSCs requires neither special pairings nor magnetic fields, such SOTI/superconductor heterostructures are outstanding platforms of Majorana modes and may have wide application in the future.