A recurring motif in unconventional superconductivity is a temperature – tuning parameter phase diagram that includes a domelike maximum in superconducting transition temperature, T_c, and some form of ordered magnetism in close proximity. In Sr₂RuO₄, uniaxial pressure applied along the <100> direction of the lattice tunes the material through a qualitatively similar set of features [1]. Our ongoing development of thermodynamic probes compatible with uniaxial pressure tuning has revealed new aspects of the low-temperature phase diagram of strained Sr₂RuO₄. Through measurements of the stress-strain relation, we found a strong coupling between the conduction electron system and the crystal lattice at the maximum in T_c, where there is a uniaxial-pressure-tuned Lifshitz transition [2]. Combining our measurements with a.c. elastocalorimetry, we have mapped out the extent of the poorly understood magnetic phase in temperature and in strain, and are now investigating the response of this phase to magnetic field.

[1] Y.-S. Li et al., Nature 607, 276 (2022).

[2] H.M.L. Noad et al., Science 382, 447 (2023).