Experimental evidence of Tc enhancement above 50 K and diode and paramagnetic-Meissner effects, in Nickelate films on highly reduced $SrTiO_3$

Abstract: Since the discovery of superconductivity in nickelate thin films in 2019, the quest for enhancing their $T_c$ has been ongoing. Here we provide experimental evidence for $T_c$ enhancement in oxygen deficient films on highly reduced and conducting $SrTiO_3$ substrates. $T_c$ onset of 50-70 K was found in Meissner and transport measurements, which indicates superconductivity in islands or domains in our films, where $T_c$ 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.