High-temperature Majorana corner modes in a d+id′ superconductor heterostructure: Application to twisted bilayer cuprate superconductors

The realization of Majorana corner modes generally requires unconventional superconducting pairing or s-wave pairing. However, the bulk nodes in unconventional superconductors and the low Tc of s-wave superconductors are not conducive to the experimental observation of Majorana corner modes. Here, we show the emergence of a Majorana corner mode at each corner of a two-dimensional topological insulator in proximity to a d+id′ pairing superconductor, such as heavily doped graphene or especially a twisted bilayer of a cuprate superconductor, e.g., Bi2Sr2CaCu2O8+δ, which has recently been proposed as a fully gapped chiral dx2-y2+idxy superconductor with Tc close to its native 90 K, and an in-plane magnetic field. By numerical calculation and intuitive edge theory, we find that the interplay of the proximity-induced pairing and Zeeman field can introduce opposite Dirac masses on adjacent edges of the topological insulator, which creates one zero-energy Majorana mode at each corner. Our scheme offers a feasible route to achieve and explore Majorana corner modes in a high-temperature platform without bulk superconductor nodes.