Abstract
Many unconventional superconductors show a similar phase diagram with different ground states, which can be tuned by external parameters, such as chemical doping or pressure. Recently, uniaxial stress, a directional probe, has shown the capabilities of tuning the electronic structures of Sr₂RuO₄ across a Van Hove singularity (VHS). In this talk I will take Sr₂RuO₄ as an example to demonstrate versatility of the uniaxial stress technique. I will present thermodynamic probes I have been developed and discuss our main findings. In short, the phase diagram of Sr₂RuO₄, remaining unknown for more than two decades, has a SC dome in proximity to a magnetic phase like many unconventional superconductors. In addition, a strong reversal of the ECE around the VHS upon entering the SC state is observed. Together with theoretical calculations, these results strongly suggest a node-less gap opening at the VHS and, thus, place a strong constraint on possible SC order parameters.