Strain-induced time reversal breaking and half quantum vortices near a putative superconducting tetracritical point in Sr2RuO4

It has been shown that many seemingly contradictory experimental findings concerning the superconducting state in Sr2RuO4 can be accounted for as resulting from the existence of an assumed tetracritical point at near-ambient pressure at which dx2−y2 and gxy(x2−y2) superconducting states are degenerate. We perform both a Landau-Ginzburg and a microscopic mean-field analysis of the effect of spatially varying strain on such a state. In the presence of finite xy shear strain, the superconducting state consists of two possible symmetry-related time-reversal symmetry (TRS) preserving states d±g. However, at domain walls between two such regions, TRS can be broken, resulting in a d+ig state. More generally, we find that various natural patterns of spatially varying strain induce a rich variety of superconducting textures, including half-quantum fluxoids. These results may resolve some of the apparent inconsistencies between the theoretical proposal and various experimental observations, including the suggestive evidence of half-quantum vortices.