$T_c$ and the elastocaloric effect of Sr$_2$RuO$_4$ under $\langle 110 \rangle$ uniaxial stress: no indications of transition splitting

TL;DR

This study investigates the superconducting transition and elastocaloric response of Sr2RuO4 under uniaxial stress, finding no evidence of transition splitting or secondary transition, challenging some previous interpretations of its order parameter.

Contribution

The paper provides experimental evidence that challenges the existence of transition splitting in Sr2RuO4 under shear stress, questioning the two-component order parameter hypothesis.

Findings

No cusp observed in $T_c$ under shear stress.

No second transition detected in elastocaloric measurements.

Results are inconsistent with homogeneous time reversal symmetry breaking.

Abstract

There is considerable evidence that the superconductivity of Sr2RuO4 has two components. Among this evidence is a jump in the shear elastic modulus $c_{66}$ at the critical temperature $T_c$, observed in ultrasound measurements. Such a jump is forbidden for homogeneous single-component order parameters, and implies that $T_c$ should develop as a cusp under the application of shear strain with $\langle 110 \rangle$ principal axes. This shear strain should split the onset temperatures of the two components, if they coexist, or select one component if they do not. Here, we report measurements of $T_c$ and the elastocaloric effect of Sr2RuO4 under uniaxial stress applied along the $[110]$ lattice direction. Within experimental resolution, we resolve neither a cusp in the stress dependence of $T_c$, nor any second transition in the elastocaloric effect data. We show that reconciling these null results with the observed jumps in $c_{66}$ requires extraordinarily fine tuning to a triple point of the Ginzburg-Landau parameter space. In addition, our results are inconsistent with homogeneous time reversal symmetry breaking at a temperature $T_2 \leq T_c$ as identified in muon spin relaxation experiments.