Following the discovery of superconductivity at 1.5 K, the exact nature of the pairing mechanism in Sr2RuO4 has attracted a great deal of interest [1]. The main reason is that superconductivity appears to be highly unconventional, with spin-triplet pairing and possibly a p-wave order parameter, as opposed to the singlet d-wave pairing seen in the cuprate high-Tc. Although it is now widely accepted that superconductivity in Sr2RuO4 is mediated by spin fluctuations, their exact nature is still unresolved (i.e., either antiferromagnetic or ferromagnetic). Intriguing is also the variety of different magnetic properties that can be found across the Ca2-xSrxRuO4 phase diagram, which could hint at the nature of the superconducting paring mechanism itself [2].
In this regard, important insights could come from the study of the doping evolution of electronic and magnetic correlations in Ca2-xSrxRuO4 by (spin-resolved) ARPES. This would be the natural continuation of our detailed investigation (Fig.1) of the electronic structure of Sr2RuO4 [3], which allowed us to quantify the effect of the electronic and/or magnetic correlations, and test the intriguing hypothesis of a coexistence of superconductivity and surface ferromagnetism [4].
Furthermore, low-temperature X-ray absorption experiments on Sr2RuO4 in the superconducting state (i.e., at temperature as low as 200 mK) have already been planned on the BACH beamline at the synchrotron in Trieste (Elettra). This study, in which core electrons are excited into the unoccupied valence band states, could provide us with crucial insights on the change of symmetry of the electronic wave functions across the superconducting phase transition.