Experimental evidence of Tc enhancement above 50 K and diode and paramagnetic-Meissner effects, in Nickelate films on highly reduced SrTiO₃

Since the discovery of superconductivity in nickelate thin films in 2019, the quest for enhancing their Tc has been ongoing. Here we provide experimental evidence for Tc enhancement in oxygen deficient films on highly reduced and conducting SrTiO₃ substrates. Tc onset of 50-70 K was found in Meissner and transport measurements, which indicates superconductivity in islands or domains in our films, where Tc of zero resistance is obtained at 20-25 K. In addition, we observed a giant paramagnetic-Meissner effect peak at about 48 K, which further supports the existence of a superconductive transition just above it. Furthermore, an asymmetric or nonreciprocal and non-hysteretic superconductive diode effect was observed. The later could be fully polarized, and its polarity could be reversed. In our films we identified the infinite-layer 112 and the perovskite 113 phases, with a variety of oxygen stoichiometries in between.