The superconducting state of Sr₂RuO₄ was once thought to be a leading candidate for p-wave superconductivity.  A constant Knight shift below the transition temperature provided evidence for spin-triplet pairing, and a π phase shift observed in Josephson junction tunneling experiments suggested odd-parity pairing [1], both of which are described by p-wave states.  However, with recent experiments observing a significant decrease in the Knight shift below the transition temperature, signifying a spin-singlet state, the odd-parity results are left to be reconciled.  In this work, we show that an even-parity pseudospin-singlet state originating from interorbital pairing via spin-orbit coupling can explain what has been assumed to be evidence for an odd-parity state [2].  Further, we discuss how these experiments may be used to differentiate the proposed pairing states of Sr₂RuO₄.

 

[1] K. D. Nelson, Z. Mao, Y. Maeno, and Y. Liu, Science 306, 1151 (2004).

[2] A. W. Lindquist and H. Y. Kee, arXiv:2210.00554 (2022).