Evidence for Clean d-wave Superconductivity in Samarium Nickelates

TL;DR

This study provides evidence of clean-limit d-wave superconductivity in samarium nickelates, revealing a linear temperature dependence of superfluid density and a weak-coupling superconducting gap, similar to cuprates.

Contribution

It demonstrates the presence of clean-limit d-wave pairing in samarium nickelates using ultrafast terahertz spectroscopy, a novel insight into their superconducting mechanism.

Findings

Superfluid density decreases linearly with temperature.

Superconducting gap of 2.5 meV consistent with weak-coupling.

Clean-limit behavior confirmed by mean free path to coherence length ratio.

Abstract

The discovery of superconducting nickelates provides a unique opportunity to explore the pairing mechanism of high-temperature superconductivity. Here, we use ultrafast terahertz spectroscopy to probe the temperature-dependent superfluid density in an infinite-layer samarium nickelate film with a Tc of 20 K. The superfluid density decreases linearly with rising temperature, consistent with clean limit d-wave pairing. From this linear relation, we extract a superconducting gap of 2.5 meV and a gap-to-Tc ratio of 3, suggesting that this sample lies in the weak-coupling limit. Furthermore, the ratio of the mean free path to the coherence length, is determined to be 1.5, confirming the clean-limit behavior. These findings establish strong parallels between the pairing mechanisms in nickelate and cuprate superconductors.