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

Bai Yang Wang: Danfeng Li, Berit H. Goodge, Kyuho Lee, Motoki Osada, Shannon P. Harvey, Lena F. Kourkoutis, Malcolm R. Beasley & Harold Y. Hwang; Nature Physics, 01/04/21.

Additional Authors: Danfeng Li, Berit H. Goodge, Kyuho Lee, Motoki Osada, Shannon P. Harvey, Lena F. Kourkoutis, Malcolm R. Beasley & Harold Y. Hwang

Abstract:

The recent observation of superconductivity in thin-film infinite-layer nickelates1,2,3 offers a different angle from which to investigate superconductivity in layered oxides4. A wide range of candidate models have been proposed5,6,7,8,9,10, 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.