Effects of orbital selective dynamical correlation on the spin susceptibility and superconducting symmetries in Sr$_2$RuO$_4$

Abstract

We investigate the connection between the local electron correlation and the momentum dependence of the spin susceptibility and the superconducting gap functions in Sr$_2$RuO$_4$, using density-functional theory combined with dynamical mean-field theory. Adopting frequency-dependent twoparticle vertex moves the zero energy spin susceptibility peaks towards the Brillouin zone center, compared with random-phase approximation which basically retains the peak positions closer to the Brillouin zone boundary as determined by the Fermi-surface nesting. We find that dxy orbital plays a central role here via its enhanced correlation strength. Solving the linearized Eliashberg equation from this spin susceptibility, prime candidates of the superconducting gap symmetry are a s-wave, along with a nearly degenerate d-wave solution, all in spin singlet. Furthermore, another set of degenerate spin singlet gap functions emerges, odd with respect to k-point as well as orbital exchanges. We show that the stability of these gap functions are strongly dependent on the peak position of the spin susceptibility in the Brillouin zone.