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.
@article{arxiv.2512.20928,
title = {Evidence for Clean d-wave Superconductivity in Samarium Nickelates},
author = {Qingming Huang and Xiaofang Fu and Junlong Wu and Laifeng Li and Liang Qiao and Ye Yang},
journal= {arXiv preprint arXiv:2512.20928},
year = {2025}
}