Superconducting Gaps in Highly Compressed Ruddlesden–Popper Nickelate La4Ni3O10 – δ

The discovery of high-temperature superconductivity in Ruddlesden–Popper (RP) nickelates Lan + 1NinO3n + 1 (n = 2, …, 5) 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 to clarify 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 that can be used to extract some of the main parameters of any superconductor. Recently Peng et al. (2025) reported in-plane, and out-of-plane temperature dependent upper critical field datasets measured at wide temperature ranges in La4Ni3O10 – δ 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 of 3.7–4.3). The smaller gap has the ratio of about 1.0. Deduced ratios are in the same ballpark as those at ambient pressure MgB2.