Antiunitary symmetry protected higher-order topological phases

This article introduces the notion of antiunitary symmetry protected two-dimensional higher-order topological (HOT) Dirac insulators for charged and Majorana fermions. This construction suggests that the p+id HOT superconductor can be stable even in the presence of weak s-wave pairing and Zeeman coupling, which can be tuned by applying external strain and magnetic field, respectively. The author also shows that 3D HOT Weyl semimetals, displaying linear touching of Kramers nondegenerate bands and supporting one-dimensional Hinge modes, can be engineered by stacking such 2D antiunitary HOT insulators in the reciprocal space.