Effect of band structure on the symmetry of superconducting states

Effects of band structure oil the symmetry of superconducting (SC) states are studied. We show that various symmetries of SC status are Possible within the same type of interaction when the shape of the Fermi surface is changed. As a simple model we consider a square lattice system with a nearest-neighbor attractive interaction. and find that the spin-triplet ((p(x) + ip(y))-wave) and spin-singlet (d- or s-wave) SC states, and states with their coexistence (d + ip(y), s + ip(y)) call be stabilized if the electron density (and thus the Fermi surface) is changed. By taking into account the interlayer attractive interaction in this model, the stability of interlayer-pairing states with line nodes is examined, and its relation to the SC state of Sr2RuO4 is discussed.