High sensitivity heat capacity measurements on Sr2RuO4 under uniaxial pressure

TL;DR

This study uses high-precision heat capacity measurements under uniaxial pressure to investigate the nature of the superconducting order parameter in Sr2RuO4, providing constraints on theoretical models.

Contribution

It presents the first direct heat capacity measurements under uniaxial pressure on Sr2RuO4, constraining the possible order parameters of its superconductivity.

Findings

No clear evidence of a second superconducting transition.

Heat capacity jump increases smoothly with pressure.

Results favor order parameters maximizing near the van Hove singularity.

Abstract

A key question regarding the unconventional superconductivity of Sr$_2$RuO$_4$ remains whether the order parameter is single- or two-component. Under a hypothesis of two-component superconductivity, uniaxial pressure is expected to lift their degeneracy, resulting in a split transition. The most direct and fundamental probe of a split transition is heat capacity. Here, we report measurement of heat capacity of samples subject to large and highly homogeneous uniaxial pressure. We place an upper limit on the heat-capacity signature of any second transition of a few per cent of that of the primary superconducting transition. The normalized jump in heat capacity, $\Delta C/C$, grows smoothly as a function of uniaxial pressure, favouring order parameters which are allowed to maximize in the same part of the Brillouin zone as the well-studied van Hove singularity. Thanks to the high precision of our measurements, these findings place stringent constraints on theories of the superconductivity of Sr$_2$RuO$_4$.