Distinct reduction of Knight shift in superconducting state of Sr${}_2$RuO${}_4$ under uniaxial strain

Abstract

Shortly after the discovery of superconductivity in Sr${}_2$RuO${}_4$, spin-triplet pairing was proposed and further corroborated by a constant Knight shift ($K$) across the transition temperature (T${}_c$). However, a recent experiment observed a drop in $K$ at T${}_c$ which becomes larger under uniaxial strain, ruling out several spin-triplet scenarios. Here we show that inter-orbital spin-triplet pairing features 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 vs.~singlet pairing.

4 pages, 4 figures + 4 pages, 3 figures (Supplementary Material)