Superconducting Gaps in Pressurized Ruddlesden-Popper Nickelate La₄Ni₃O_10-δ

The experimental discovery of high-temperature superconductivity in Ruddlesden-Popper (RP) nickelates Lan+1NinO3n+1 (n = 2, 3, 4) under pressure, as well as the observation of a state with zero resistance at T ~10 K in thin films of (La,Pr)n+1NinO3n+1 (n = 2) at ambient pressure initiated a wide range of experimental and theoretical studies aimed at clarifying the nature of the occurrence of the superconducting state in RP nickelates. The upper critical field, Bc2(T), is one of two fundamental fields of any type II superconductor which can be used to extract some of the main parameters of a given superconductor. Recently, Peng et al (arXiv:2502.14410) reported in-plane, and out-of-plane temperature dependent upper critical field datasets measured at wide temperature ranges in La4Ni3O10-d single crystals pressurized at P = 48.6 GPa and P = 50.2 GPa. Here, the reported Bc2(T) data were analyzed, and it was found that the compressed nickelate La4Ni3O10-δ exhibits two-band s-wave superconductivity. Derived parameters showed that both gaps are almost isotropic. The larger gap has a moderate level of coupling strength (with a gap-to-transition temperature ratio 3.7 < 2ΔL/kBTc < 4.3). The smaller gap has the ratio of 1.0 < 2ΔS/kBTc < 1.1. Deduced ratios are in the same ballpark as those in ambient pressure MgB2.