Distinct reduction of Knight shift in superconducting state of Sr2RuO4 under uniaxial strain

Abstract

Shortly after the discovery of superconductivity in Sr2RuO4, spin-triplet pairing was proposed and further corroborated by a constant Knight shift (K) across the transition temperature (Tc). However, a recent experiment observed a drop in K at Tc which becomes larger under uniaxial strain, ruling out several spin-triplet scenarios. Here we show that even parity interorbital spin-triplet pairing can feature a d vector that rotates when uniaxial strain is applied, leading to a larger drop in the spin polarization perpendicular to the strain direction, distinct from spin-singlet pairing. We propose that anisotropic spin polarization under strain will ultimately differentiate triplet versus singlet pairing.