Constraints on the superconducting state of Sr₂RuO₄ from elastocaloric measurements

Strontium ruthenate Sr2RuO4 is an unconventional superconductor whose pairing symmetry has not been fully clarified, despite more than two decades of intensive research. Recent NMR Knight shift experiments have rekindled the Sr2RuO4 pairing debate by giving strong evidence against all odd-parity pairing states, including chiral p-wave pairing that was for a long time the leading pairing candidate. Here, we exclude additional pairing states by analyzing recent elastocaloric measurements [Y.S. Li et al., Nature 607, 276 (2022)]. To be able to explain the elastocaloric experiment, we find that unconventional even-parity pairings must include either large d(x2-y2)-wave or large {d(xz) vertical bar d(yz)}-wave admixtures, where the latter possibility arises because of the body-centered point group symmetry. These {d(xz) vertical bar d(yz)}-wave admixtures take the form of distinctively body-centered-periodic harmonics that have horizontal line nodes. Hence g(xy(x2-y2))-wave and d(xy)-wave pairings are excluded as possible dominant even pairing states.