Evidence for nodal superconductivity in infinite-layer nickelates.

Harvey, Shannon P; Wang, Bai Yang; Fowlie, Jennifer; Osada, Motoki; Lee, Kyuho; Lee, Yonghun; Li, Danfeng; Hwang, Harold Y · Proc Natl Acad Sci U S A · 2025

basic_science · Level V

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Abstract

Infinite-layer nickelates present a new family of potential unconventional superconductors. A key open question is the superconducting pairing symmetry. We present low-temperature measurements of the magnetic penetration depth in optimally doped La<sub>0.8</sub>Sr<sub>0.2</sub>NiO<sub>2</sub>, Pr<sub>0.8</sub>Sr<sub>0.2</sub>NiO<sub>2</sub>, Nd<sub>0.8</sub>Sr<sub>0.2</sub>NiO<sub>2</sub>, and Nd<sub>0.7875</sub>Sr<sub>0.2125</sub>NiO<sub>2</sub>. For La- and Pr-nickelates, the superfluid density shows a quadratic temperature dependence, indicating nodal superconductivity in the presence of disorder. Nd-nickelate exhibits complex low-temperature behavior associated with Nd 4<i>f</i> magnetism, which precludes a direct measure of the nodal structure.