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 Sr 2 RuO 4 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 Sr 2 RuO 4 in detail and narrowed down possible superconducting (SC) order parameters. We summarize our main findings, as many unconventional superconductors, Sr 2 RuO 4 has a SC dome in proximity to a magnetic phase. Both ECE and HC exhibit no signature of a second transition below T c . 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.
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[2] V. Sunko et al. npj Quant. Mat. 4, 2397–4648 (2019).
[3] Y.-S. Li et al. Nature 607, 276–280 (2022).
[4] Y.-S. Li et al. Proc. Natl. Acad. Sci. USA 118, e2020492118 (2021).