Isotropic Pauli-Limited Superconductivity in the Infinite Layer Nickelate Nd$_{0.775}$Sr$_{0.225}$NiO$_{2}$

Bai Yang Wang; Danfeng Li; Berit H. Goodge; Kyuho Lee; Motoki Osada; Shannon P. Harvey; Lena F. Kourkoutis; Malcolm R. Beasley; Harold Y. Hwang

doi:10.1038/s41567-020-01128-5

arXiv · 2012.06560

Isotropic Pauli-Limited Superconductivity in the Infinite Layer Nickelate Nd$_{0.775}$Sr$_{0.225}$NiO$_{2}$

Bai Yang Wang·Danfeng Li·Berit H. Goodge·Kyuho Lee·Motoki Osada·Shannon P. Harvey·Lena F. Kourkoutis·Malcolm R. Beasley·Harold Y. Hwang

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Abstract

The recent observation of superconductivity in thin film infinite-layer nickelates$^{1-3}$ offers a different angle to investigate superconductivity in layered oxides$^{4}$. A wide range of candidate models have been proposed$^{5-10}$, emphasizing single- or multi-orbital electronic structure, Kondo or Hund's coupling, and analogies to cuprates. Clearly, 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 Nd$_{0.775}$Sr$_{0.225}$NiO$_{2}$. 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.

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Bai Yang Wang, Danfeng Li, Berit H. Goodge, Kyuho Lee, Motoki Osada, Shannon P. Harvey, Lena F. Kourkoutis, Malcolm R. Beasley, Harold Y. Hwang. 2020-12-11. Isotropic Pauli-Limited Superconductivity in the Infinite Layer Nickelate Nd$_{0.775}$Sr$_{0.225}$NiO$_{2}$. https://doi.org/10.1038/s41567-020-01128-5

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