A crib-shaped triplet pairing gap function for an orthogonal pair of quasi-one dimensional Fermi surfaces in Sr$_2$RuO$_4$

Abstract

The competition between spin-triplet and singlet pairings is studied theoretically for the tight-binding $\alpha$-$\beta$ bands in Sr$_2$RuO$_4$, which arise from two sets of quasi-one dimensional Fermi surfaces. Using multiband FLEX approximation, where we incorporate an anisotropy in the spin fluctuations as suggested from experiments, we show that (i) the triplet can dominate over the singlet (which turns out to be extended s), and (ii) the triplet gap function optimized in the Eliashberg equation has an unusual, very non-sinusoidal form, whose time-reversal-broken combination exhibits a crib-shaped amplitude with dips.Comment: 5 pages, RevTeX, to appear in Phys.Rev.B (Rapid Communications