Two superconducting components with different symmetries in Nd1-xSrxNiO2 films

TL;DR

This study presents tunneling measurements on Nd1-xSrxNiO2 films, revealing two distinct superconducting gap symmetries, indicating unconventional superconductivity similar to cuprates.

Contribution

First single-particle tunneling data on nickelate superconductors showing coexistence of different gap symmetries, highlighting their unconventional nature.

Findings

Identification of d-wave gap with 3.9 meV maximum

Observation of a full gap of 2.35 meV

Evidence of mixed gap contributions in some spectra

Abstract

The pairing mechanism in cuprates remains as one of the most challenging issues in the field of condensed matter physics. The unique 3d9 electron orbital of the Cu2+ ionic states in cuprates is supposed to be the major player for the occurrence of superconductivity. Recently, superconductivity at about 9-15 K was discovered in infinite layer thin films of nickelate Nd1-xSrxNiO2 (x=0.1-0.2) which is believed to have the similar 3d9 orbital electrons. The key issue concerned here is about the superconducting gap function. Here we report the first set data of single particle tunneling measurements on the superconducting nickelate thin films. We find predominantly two types of tunneling spectra, one shows a V-shape feature which can be fitted very well by a d-wave gap function with gap maximum of about 3.9 meV, another one exhibits a full gap of about 2.35 meV. Some spectra demonstrate mixed contributions of these two components. Our results suggest that the newly found Ni-based superconductors play as close analogs to cuprates, and thus demonstrate the commonality of unconventional superconductivity.