Topological superconductivity in multiorbital materials

Abstract: Multiorbital materials add a new intricacy to the already complex phenomenon of superconductivity. The additional orbital degree of freedom requires leaving behind the established band picture, but also opens the possibility of more complicated order parameters with new properties. This thesis summarizes theoretical studies of two examples of multiorbital superconductors.The first part focuses on superconductivity in Kitaev materials. The unusual interactions in these materials are shown to give rise to spin triplet superconducting pairing on both two-and three-dimensional lattice structures. A symmetry characterization enables the analysis of the stable superconducting order parameters, revealing several nodal states on the 3D harmonic honeycomb lattices and a competition between nematic and chiral superconductivity on the 2D honeycomb lattice. The following topological classification uncovers a number of topologically non-trivial superconducting states protected by various symmetries, giving rise to flat bands, Fermi arcs, or dispersing Majorana excitations on their surface.The thesis’ second part spotlights odd-frequency superconductivity in a doped topological insulator. An experimentally supported uncommon interorbital order parameter gives rise to large intraorbital odd-frequency pairing. A calculation of the Meissner effect unveils an unexpected diamagnetic odd-frequency Meissner response, stabilizing superconductivity.The results of this thesis highlight the diverse nature of superconductivity in multiorbitalmaterials and stimulate further research on its topological properties and stability.