Abstract:
Many intriguing unconventional superconductors display a phase diagram containing strongly correlated states, which can be tuned by external parameters, such as chemical doping or pressure. In recent years, uniaxial pressure, which can break the symmetry of the crystal lattice, has shown the capabilities of tuning the electronic structures of Sr2RuO4 across a Van Hove singularity (VHS) [1, 2]. By performing high precision ac-elastocaloric effect (ECE) [3] and ac-heat capacity (HC) [4] measurements under uniaxial pressure along the [100] direction, we mapped out the phase diagram of Sr2RuO4 in detail and narrowed down possible superconducting (SC) order parameters. We summarize our main findings, as many unconventional superconductors, Sr2RuO4 has a SC dome in proximity to a magnetic phase. Both ECE and HC exhibit no signature of a second transition below Tc. Besides, we observe a strong reversal of the ECE around the VHS upon entering the SC state. Together with a model calculation, these results strongly suggest a node-less gap opening at the VHS and, thus, put a strong constraint on possible SC order parameters.