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(0.8)Sr(0.2)NiO(2), Pr(0.8)Sr(0.2)NiO(2), Nd(0.8)Sr(0.2)NiO(2), and Nd(0.7875)Sr(0.2125)NiO(2). 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.