Abstract
We investigate superconductivity in a two-orbital Hubbard model on a square lattice by applying fluctuation exchange approximation. In the present model, the symmetry of the two orbitals are assumed to be that of an $s$ orbital. Then, we find that an $s$-wave spin-triplet orbital-antisymmetric state and a $p$-wave spin-singlet orbital-antisymmetric state appear when Hund's rule coupling is large. These states are prohibited in a single-orbital model within states with even frequency dependence, but allowed for multiorbital systems. We also discuss pairing symmetry in other models which are equivalent to the two-orbital Hubbard model except for symmetry of orbitals. Finally, we show that pairing states with a finite total momentum, even without a magnetic field, are possible in a system with two Fermi surfaces.
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