Evidence for nodal superconductivity in infinite-layer nickelates

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_0.8Sr_0.2NiO₂, Pr_0.8Sr_0.2NiO₂, Nd_0.8Sr_0.2NiO₂, and Nd_0.7875Sr_0.2125NiO₂. 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 4f magnetism, which precludes a direct measure of the nodal structure.