The recently emerging superconductivity in infinite-layer nickelates with the isostructural and isoelectronic characteristics of cuprates provides a new platform to explore the pairing mechanism of high-temperature superconductors. In this work, we studied the upper critical field $\left(H_{\mathrm{c}2}\right)$ of a high-quality ${\mathrm{La}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$ thin film with superconducting transition temperature, $T_{\mathrm{c}}^{\mathrm{onset}}=18.8$ K, using high magnetic field up to 56 T. A very large $H_{\mathrm{c}2}, \sim 40$ T for $H\parallel c$ and $\sim 52$ T for $H\perp c$, was confirmed, which suggests that infinite-layer nickelates also have great application potential. The anisotropy of $H_{\mathrm{c}2}$ monotonically decreases from $\sim 10(\gamma =H_{\mathrm{c}2}^{ab}/H_{\mathrm{c}2}^c)$ near $T_{\mathrm{c}}$ to $\sim 1.5$ at 2 K. Angle dependence of $H_{\mathrm{c}2}$ confirms the crossover of superconductivity from two-dimensional to three-dimensional as the temperature decreases. We discussed that the interstitial orbital effect causes the weakening of anisotropy. The observed abnormal upturning of $H_{\mathrm{c}2}$ at low temperatures is found to be a universal behavior independent of film quality and rare-earth elements. Therefore, it should not be the Fulde-Ferrell-Larkin-Ovchinnikov state due to the fact that it is in the dirty limit and insensitive to disorder.

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• High magnetic fields
• Multiband superconductivity
• Superconductivity
• High-temperature superconductors
• Type-II superconductors
• Unconventional superconductors
• Critical field
• Resistivity measurements