  We study and classify the proximity-induced superconducting pairing in a
topological insulator (TI)-superconductor (SC) hybrid structure for SCs with
different symmetries. The Dirac surface state gives a coupling between
spin-singlet and spin-triplet pairing amplitudes as well as pairing that is odd
in frequency for p-wave SCs. We also find that all SCs induce pairing that is
odd in both frequency and orbital (band) index, with oddness in frequency and
orbital index being completely interchangeable. The different induced pairing
amplitudes significantly modifies the density of states in the TI surface
layer.
