Observation of Josephson-like tunneling junction characteristics and positive magnetoresistance in Oxygen deficient Nickelate films of $N{d}_{0.8}S{r}_{0.2}Ni{O}_{3-\delta }$

Abstract

Nickelate films have recently attracted broad attention due to the observation of superconductivity in the infinite layer phase of $N{d}_{0.8}S{r}_{0.2}Ni{O}_2$ (obtained by reducing Sr doped $NdNi{O}_3$ films) and their similarity to the cuprates high temperature superconductors. Here we report on the observation of a new type of transport in oxygen poor $N{d}_{0.8}S{r}_{0.2}Ni{O}_{3-\delta }$ films. At high temperatures, variable range hopping is observed while at low temperatures a novel tunneling behavior is found where Josephson-like tunneling junction characteristic with serial resistance is revealed. We attribute this phenomenon to coupling between superconductive (S) surfaces of the grains in our Oxygen poor films via the insulating (I) grain boundaries, which yields SIS junctions in series with the normal (N) resistance of the grains themselves. The similarity of the observed conductance spectra to tunneling junction characteristic with Josephson-like current is striking, and seems to support the existence of superconductivity in our samples.

This version includes: 1. A new Fig, 1 with the surface morphology and a surface tunneling model. 2. Fig. 2 of the XRD now shows more details including minority Ni_xO_y phases. 3. More VRH models are now included in Fig. 4. 4. Extended conductance range in Fig. 6 (c) now shows the second quasi-particle branch more clearly

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