What is the superconducting order parameter of Sr2RuO4
In plain words
The pairing pattern of Sr2RuO4 must explain conflicting data: some measurements suggest a two-part order that breaks time-reversal symmetry, while others see only one transition.
Precise statement
Determine the order parameter of Sr2RuO4 ($T_c = 1.5\,\mathrm{K}$): parity, spin structure, orbital and band content, and irreducible representation of D4h, consistent with the drop of the 17O Knight shift for in-plane fields (2019), the ultrasound jump in shear modulus $c66$ suggesting two components, muSR and polar Kerr time-reversal breaking, and no second heat-capacity anomaly under uniaxial stress. Candidates include d_xz + i d_yz, s' + i d_x2-y2, d + i g and interorbital pairing states.
What would settle it
A single order parameter that quantitatively fits Knight shift, ultrasound, muSR, Kerr and strain-dependent heat capacity, confirmed by a phase-sensitive measurement.
Related problems
- More general than Location of gap nodes on the Sr2RuO4 Fermi sheets
- More general than Is time-reversal breaking in Sr2RuO4 an intrinsic bulk property
- More general than Is the Sr2RuO4 order parameter two-component