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.
Highlights
The discovery of superconductivity in Sr2RuO4 [1] has had great attention over the past two decades
Even-parity spin-triplet pairings are allowed when the pairing occurs between different orbitals with the antisymmetric fermionic wavefunction condition, i.e., orbital singlets
The idea of orbital-singlet spin-triplet (OSST) pairing is not limited to the atomic (s-wave) spin-orbit coupling (SOC) leading to an s-wave gap with the A1g representation
Summary
Distinct reduction of Knight shift in superconducting state of Sr2RuO4 under uniaxial strain. Lindquist and Hae-Young Kee1,2,* 1Department of Physics and Center for Quantum Materials, University of Toronto, 60 St. George St., Toronto, Ontario, Canada M5S 1A7. 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). A recent experiment observed a drop in K at Tc which becomes larger under uniaxial strain, ruling out several spin-triplet scenarios. 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 differentiate triplet versus singlet pairing
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