Two-particle Berry phase mechanism for Dirac and Majorana Kramers pairs of corner modes

We uncover an alternative two-particle Berry phase mechanism to realize exotic corner modes in second-order topological insulators (TIs) and topological superconductors (TSCs) with time-reversal symmetry. We show that the nontrivial pseudospin textures of edge states in two different types of two-dimensional TIs give rise to different two-particle geometric phases in the particle-hole and particle-particle channels, respectively, for which the edge mass domain walls or intrinsic pi junctions emerge across corners when an external magnetic field or s-wave superconductivity is considered, hosting Dirac or Majorana corner modes. Remarkably, with this mechanism we predict the Majorana Kramers pair of corner modes by directly coupling the edge of a type-II time-reversal invariant TI to a uniform s-wave SC, in sharp contrast to previous proposals which rely on unconventional SC pairing or a complex setting for a fine-tuned SC pi junction. We find Au/GaAs(111) to be a realistic material candidate for realizing such a Majorana Kramers pair of corner modes.