Order parameter in superconductors with nondegenerate bands

In noncentrosymmetric metals, the spin degeneracy of the electronic bands is lifted by spin-orbit coupling. We consider general symmetry properties of the pairing function Δ(k) in noncentrosymmetric superconductors with spin-orbit coupling (NSC), including CePt₃Si, UIr, and Cd₂Re₂O₇. We find that Δ(k)=χ(k)t(k), where χ(k) is an even function which transforms according to the irreducible representations of the crystallographic point group and t(k) is a model-dependent phase factor. We consider tunneling between a NSC and a conventional superconductor. It is found that, in terms of thermodynamical properties as well as the Josephson effect, the state of NSC resembles a singlet superconducting state with gap function χ(k).