FLEX modeling of the strain dependence of the superconducting state of Sr₂RuO₄

We apply the fluctuation exchange approximation (FLEX) to model the evolution of the superconducting state of Sr₂RuO₄ under strain. Using first-principles-based parameters for band-structure, spin-orbit coupling and electron-electron interactions, FLEX produces a d_x²-y² state on the γ-band in the unstrained limit, with minor p-wave and α- and β-band contributions induced by spin-orbit coupling. As is observed experimentally, FLEX results show a steep drop-off in T_c when strain pushes a γ-band van Hove singularity through and below the Fermi level. However, the model produces a weaker dependence of T_c at low strain levels than is reported experimentally. For temperatures below T_c we have yet to observe a secondary transition that incorporates a component that is nearly-degenerate to the dominant pairing state, though lower-temperature simulations are ongoing. We also report results for the spin susceptibility below T_c.