Physical Properties Revealed by Transport Measurements for Superconducting Nd0.8Sr0.2NiO2 Thin Films

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 H-beta |cos theta| (beta = 6-1), with theta 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.

Automated summary

The discovery of superconductivity in infinite-layer nickelate superconducting films has sparked interest due to similarities with high-T(c) cuprate superconductors. Experimental data on these films, specifically regarding the upper critical field, remain limited. This study presents temperature- and angle-dependence of resistivity in Nd0.8Sr0.2NiO2 thin films, revealing information on superconductivity anisotropy and paramagnetic effects.