Isotropic Pauli-limited superconductivity in the infinite-layer nickelate Nd0.775Sr0.225NiO2

The recent observation of superconductivity in thin-film infinite-layer nickelates(1-3) offers a different angle from which to investigate superconductivity in layered oxides(4). A wide range of candidate models have been proposed(5-10), which emphasize single- or multi-orbital electronic structure, Kondo or Hund's coupling and analogies to cuprates. Further experimental characterization of the superconducting state is needed to develop a full understanding of the nickelates. Here we use magnetotransport measurements to probe the superconducting anisotropy in Nd0.775Sr0.225NiO2. We find that the upper critical field is surprisingly isotropic at low temperatures despite the layered crystal structure. In a magnetic field, the superconductivity is strongly Pauli-limited, such that the paramagnetic effect dominates over orbital de-pairing. Underlying this isotropic response is a substantial anisotropy in the superconducting coherence length, which is at least four times longer in-plane than out-of-plane. A prominent low-temperature upturn in the upper critical field indicates the presence of an unconventional ground state. Measurements of a superconducting infinite-layer nickelate show that its upper critical field is largely isotropic despite its quasi-two-dimensional structure. This indicates that, unusually for layered oxides, the superconductivity is Pauli-limited.

Automated summary

Recent studies have observed superconductivity in nickelates, prompting the proposal of various candidate models to understand this phenomenon. By using magnetotransport measurements, researchers were able to probe the superconducting anisotropy in nickelates and found surprising isotropy in the upper critical field despite the layered crystal structure. This suggests that the superconductivity in nickelates is Pauli-limited, unlike traditional layered oxides.