Majorana Kramers Pairs in Higher-Order Topological Insulators*

We propose a tune-free scheme to realize Majorana bound states using higher-order topological insulators [1]. When two hinges of a higher-order topological insulator nanowire are brought into the proximity of an s-wave superconductor, two types of pairings arise, one being local (intra-hinge) pairing and the other nonlocal (inter-hinge) pairing. We find that, the competition between these pairings leads to a topological phase transition. The energy band is inverted in the regime where the nonlocal pairing dominates over the local one, leading to the formation of a Kramers pair of Majorana bound states at each end of the nanowire. We show that this topological condition can be fulfilled in the presence of moderate electron-electron interactions, without fine-tuning system parameters such as external magnetic fields.

[1] Chen-Hsuan Hsu, Peter Stano, Jelena Klinovaja, and Daniel Loss, Phys. Rev. Lett. 121, 196801 (2018).