Physical Properties Revealed by Transport Measurements for Superconducting Nd0.8Sr0.2NiO2 Thin FilmsSupported by the National Key R&D Program of China (Grant Nos. 2016YFA0300401 and 2018YFA0704202), the National Natural Science Foundation of China (Grant Nos. 12061131001, 11774153, and 1861161004), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB25000000), and the Fundamental Research Funds for the Central Universities (Grant

Abstract

The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention, largely because their crystalline and electronic structures are similar to those of high-T c cuprate superconductors. The upper critical field can provide a great deal of information on the subject of superconductivity, but detailed experimental data are still lacking for these films. We present the temperature- and angle-dependence of resistivity, measured under different magnetic fields H in Nd0.8Sr0.2NiO2 thin films. The onset superconducting transition occurs at about 16.2 K at 0 T. Temperature-dependent upper critical fields, determined using a criterion very close to the onset transition, show a clear negative curvature near the critical transition temperature, which can be explained as a consequence of the paramagnetically limited effect on superconductivity. The temperature-dependent anisotropy of the upper critical field is obtained from resistivity data, which yields a value decreasing from 3 to 1.2 with a reduction in temperature. This can be explained in terms of the variable contribution from the orbital limit effect on the upper critical field. The angle-dependence of resistivity at a fixed temperature, and at different magnetic fields, cannot be scaled to a curve, which deviates from the prediction of the anisotropic Ginzburg–Landau theory. However, at low temperatures, the resistance difference can be scaled via the parameter Hβ |cosθ| (β = 6–1), with θ being the angle enclosed between the c-axis and the applied magnetic field. As the first detailed study of the upper critical field of nickelate thin films, our results clearly indicate a small anisotropy, and a paramagnetically limited effect, in terms of superconductivity, in nickelate superconductors.