Random spin-orbit coupling in spin triplet superconductors. Stacking faults in Sr2RuO4 and CePt3Si

The random spin-orbit coupling in multicomponent superconductors is investigated focusing on the non-centrosymmetric superconductor CePt3Si and the spin triplet superconductor Sr2RuO4. We find novel manifestations of the random spin-orbit coupling in the multicomponent superconductors with directional disorders, such as stacking faults. The presence of stacking faults is indicated for the disordered phase of CePt3Si and Sr2RuO4. It is shown that the d-vector of spin triplet pairing is locked to be d = kyx - kxy with the anisotropy ΔTc/Tc0-α-bar2/Tc0Wz, where α-bar, Tc0, and Wz are the mean square root of random spin-orbit coupling, the transition temperature in the clean limit, and the kinetic energy along the c-axis, respectively. This anisotropy is much larger (smaller) than that in the clean bulk Sr2RuO4 (CePt3Si). These results indicate that the helical pairing state d=kyx - kxy in the eutectic crystal of Sr2RuO4-Sr3Ru2O7 is stabilized in contrast to the chiral state d=(kx±iky)z in the bulk Sr2RuO4. The unusual variation of Tc in CePt3Si is resolved by taking into account the weak pair-breaking effect arising from the uniform and random spin-orbit couplings. These superconductors provide a basis for discussing recent topics on Majorana fermions and non-Abelian statistics. (author)