Enhanced triplet superconductivity in noncentrosymmetric systems

We study pairing symmetry of noncentrosymmetric superconductors based on the extended Hubbard model on the square lattice near half-filling, using the random phase approximation. We show that $d+f$-wave pairing is favored and the triplet $f$-wave state is enhanced by Rashba-type spin-orbit coupling originating from the broken inversion symmetry. The enhanced triplet superconductivity stems from the increase of the effective interaction for the triplet pairing and the reduction of the spin susceptibility caused by the Rashba-type spin-orbit coupling which lead to the increase of the triplet component and the destruction of the singlet one, respectively.

Figure 1

(Color) Real and imaginary parts of the gap function ${\Delta }_{\uparrow \uparrow }$. We take $\lambda =0.01$ and $\lambda =0.5$ in the upper and lower figures, respectively. Solid lines represent Fermi surfaces. Arrows indicate typical scattering processes.

Figure 2

(Color) Real part of the singlet gap function ${\Delta }_s$. We take $\lambda =0.01$ and $\lambda =0.5$ in the upper and lower figures, respectively. Solid lines represent Fermi surfaces.

Figure 3

(Color online) Spin and charge susceptibilities (${\chi }_S$ and ${\chi }_C$). We set $\lambda =0.01$ and $\lambda =0.5$ in the upper and lower figures, respectively.

Figure 4

(Color online) Real part of ${\chi }_{\mathrm{lad}}^{\uparrow \downarrow }$. We set $\lambda =0.01$ and $\lambda =0.5$ in the upper and lower figures, respectively.

Figure 5

Relative magnitude of $\max \mid {\Delta }_{\uparrow \uparrow }\mid$ and $\max \mid {\Delta }_s\mid$ as a function of the strength of RSOC $\lambda$.