Single particle tunneling spectrum of superconducting Nd1-xSrxNiO2 thin films

TLDR

Superconductivity in infinite‑layer nickelate Nd1‑xSrxNiO2 thin films, which share 3d9 orbital electrons with cuprates, underscores the unresolved pairing mechanism in cuprates. The study aims to investigate the superconducting gap structure of Nd1‑xSrxNiO2 thin films using tunneling spectroscopy. Single‑particle tunneling measurements were performed on the films to probe their quasiparticle spectra. Two distinct tunneling spectra were observed: a V‑shaped d‑wave gap of about 3.9 meV and a full gap of about 2.35 meV, with some spectra showing mixed contributions, and the d‑wave component is attributed to the Ni‑3d_{x^2−y^2} orbital, indicating both similarities and differences with cuprates.

Abstract

Abstract The pairing mechanism in cuprates remains as one of the most challenging issues in condensed matter physics. Recently, superconductivity was discovered in thin films of the infinite-layer nickelate Nd 1-x Sr x NiO 2 (x = 0.12–0.25) which is believed to have the similar 3d 9 orbital electrons as that in cuprates. Here we report 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 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. Combining with theoretical calculations, we attribute the d -wave gap to the pairing potential of the $${\mathrm{Ni - }}3d_{x^2 - y^2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Ni-</mml:mi> <mml:mn>3</mml:mn> <mml:msub> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>−</mml:mo> <mml:msup> <mml:mrow> <mml:mi>y</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:msub> </mml:math> orbital. Several possible reasons are given for explaining the full gap feature. Our results indicate both similarities and distinctions between the newly found Ni-based superconductors and cuprates.