Theory of Parity Violated Cooper Pairs in Weakly Noncentrosymmetric Superconductors

We propose that in noncentrosymmetric superconductors with weakly asymmetric spin-orbit interaction the field-induced pair correlation between the spin-orbit split different bands ignored in previous studies yields unique effects; i.e. the Pauli depairing effect is anisotropic in the momentum space, and as a result, magnetic fields induce point-node-like anisotropic gap structure of the quasiparticle energy even for isotropic s-wave states, which seriously affects thermodynamic quantities at low temperatures. Also, it is shown that when the magnitude of the spin-orbit interaction is smaller than the superconducting gap, the specific heat as a function of a magnetic field exhibit a two-gap-like behavior, even when there is only a single gap. These features characterize parity violated Cooper pairs in weakly noncentrosymmetric systems. We suggest the possible detection of these effects in the superconductor with weakly broken inversion symmetry Y_2C_3.