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Mechanism of Tc enhancement in co-doped SmNiO2 thin films

Determine the microscopic mechanism by which europium and calcium co‑doping in Sm1−xSrxNiO2 thin films increases the superconducting transition temperature to approximately 40 K, including the roles of carrier concentration, epitaxial strain, and disorder introduced during growth and reduction.

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Background

In the infinite-layer nickelates, carrier doping and epitaxial strain are known to affect superconductivity. Recent reports on Sm1−xSrxNiO2 films co‑doped with Eu and Ca (SECS) show transition temperatures near 40 K and unusually low resistivity, as well as reduced c‑axis lattice parameters.

Despite these material advances, the authors explicitly state that the origin of the Tc improvement is not yet understood, motivating further experimental and theoretical work to identify the relevant mechanism(s).

References

These co-doped compounds exhibit remarkably low resistivity—on the order of 0.01 m Ω·cm—and a record-small c-axis lattice parameter. The origin of this improvement remains unclear, calling for further experimental and theoretical investigation.

— Recent progress in nickelate superconductors (2509.08386 - Wang et al., 10 Sep 2025) in Section 2 (112), item (b) Enhancement of Tc via chemical tuning; paragraph accompanying Fig. 4(b)