Random Spin-orbit Coupling in Spin Triplet Superconductors: Stacking Faults in Sr_2RuO_4 and CePt_3Si

TL;DR

This paper explores how random spin-orbit coupling affects multicomponent spin triplet superconductors like Sr_2RuO_4 and CePt_3Si, revealing novel anisotropies, pairing states, and implications for Majorana fermions.

Contribution

It demonstrates the impact of stacking faults and directional disorder on the pairing symmetry and anisotropy in these superconductors, introducing new insights into their superconducting states.

Findings

Locking of the d-vector to a specific form due to disorder

Enhanced anisotropy in the disordered phase compared to clean bulk

Stabilization of helical pairing state in Sr_2RuO_4-Sr_3Ru_2O_7 eutectic

Abstract

The random spin-orbit coupling in multicomponent superconductors is investigated focusing on the non-centrosymmetric superconductor CePt_3Si and the spin triplet superconductor Sr_2RuO_4. 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 CePt_3Si and Sr_2RuO_4. It is shown that the d-vector of spin triplet superconductivity is locked to be d = k_y x - k_x y with the anisotropy \Delta T_c/T_c0 \sim \bar{\alpha}^2/T_c0 W_z, where \bar{\alpha}, T_c0, and W_z 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 Sr_2RuO_4 (CePt_3Si). These results indicate that the helical pairing state d = k_y x - k_x y in the eutectic crystal Sr_2RuO_4-Sr_3Ru_2O_7 is stabilized in contrast to the chiral state d = (k_x \pm i k_y) z in the bulk Sr_2RuO_4. The unusual variation of T_c in CePt_3Si 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.