CM In the literature: contested

Is the Sr2RuO4 order parameter two-component

In plain words

If the order parameter has two parts, squeezing the crystal along one axis should split the superconducting transition into two; one probe sees a split and another does not.

Precise statement

Determine whether uniaxial stress along $[100]$ splits $T_c$ of Sr2RuO4 into two thermodynamic transitions, as a two-component order parameter (multidimensional representation or accidental degeneracy) requires. An answer is a thermodynamic detection of the second transition, or a bound on its specific-heat jump below the value predicted by models fitted to the ultrasound data.

What would settle it

Calorimetry or elastocaloric measurements under stress with sensitivity below the predicted second-jump size, on the same samples used for muSR.

Status in the literature

muSR under stress (2021) reported split onsets of superconductivity and time-reversal breaking, while heat capacity under stress found no second transition above a few percent of the main anomaly.