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Title: What is the superconducting order parameter of Sr2RuO4
Plain: 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: 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.
Settled by: A single order parameter that quantitatively fits Knight shift, ultrasound, muSR, Kerr and strain-dependent heat capacity, confirmed by a phase-sensitive measurement.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: contested
Status note: (empty)
Posed since: 1995