Reconciling the π phase shift in Josephson junction experiments with even-parity superconductivity in Sr2RuO4

The superconducting state of Sr$_2$RuO$_4$ was once thought to be a leading\ncandidate for $p$-wave superconductivity. A constant Knight shift below the\ntransition temperature provided evidence for spin-triplet pairing, and a $\\pi$\nphase shift observed in Josephson junction tunneling experiments suggested\nodd-parity pairing, both of which are described by $p$-wave states. However,\nwith recent experiments observing a significant decrease in the Knight shift\nbelow the transition temperature, signifying a spin-singlet state, the\nodd-parity results are left to be reconciled. In this work, we show that an\neven-parity pseudospin-singlet state originating from interorbital pairing via\nspin-orbit coupling can explain what has been assumed to be evidence for an\nodd-parity state. In the presence of small mirror symmetry breaking,\ninterorbital pairing is uniquely capable of displaying odd-parity\ncharacteristics required to explain these experimental results. Further, we\ndiscuss how these experiments may be used to differentiate the proposed pairing\nstates of Sr$_2$RuO$_4$.\n