Experimental evidence of Tc enhancement above 50 K and diode and paramagnetic-Meissner effects, in Nickelate films on highly reduced $SrTi{O}_3$

Abstract

Since the discovery of superconductivity in nickelate thin films in 2019, the quest for enhancing their ${\mathrm{T}}_{\mathrm{c}}$ has been ongoing. Here we provide experimental evidence for ${\mathrm{T}}_{\mathrm{c}}$ enhancement in oxygen deficient films on highly reduced and conducting SrTiO${}_3$ substrates. ${\mathrm{T}}_{\mathrm{c}}$ onset of 50-70 K was found in Meissner and transport measurements, which indicates superconductivity in islands or domains in our films, where ${\mathrm{T}}_{\mathrm{c}}$ 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 latter effect could be fully polarized, and its polarity could be reversed. Our mixed phase films comprised of many Ruddlesden-Popper $(\mathrm{N}{\mathrm{d}}_{0.8}\mathrm{S}{\mathrm{r}}_{0.2}{)}_{\mathrm{n}+1}\mathrm{N}{\mathrm{i}}_{\mathrm{n}}{\mathrm{O}}_{3n+1}$ phases and includes the infinite-layer (IL) phase.

In this v3 version we include new STEM results of our virgin films, and extend our analysis of all FFT-STEM results. We found that our mixed-phase films comprise of various RP and IL phases