Insufficient Structural Characterization in Ultrathin Superconducting Spin Valves as a Limitation on Transport Evidence for Solitary Superconductivity

Superconductor/ferromagnet (S/F) spin valves can switch superconductivity with the magnetic configuration. A recent experiment on an ultrathin structure with a Heusler‐alloy ferromagnet and an ultrathin Pb layer reported such switching as the first experimental realization of the solitary‐superconductivity regime, in which superconductivity survives only for antiparallel magnetizations. We argue that the reported transport data, while demonstrating a large magnetic‐configuration‐dependent response, do not by themselves single out that interpretation. Read in the form the data establish, the series is one detected transition together with a set of upper bounds; the quoted contrast is the endpoint of an admissible interval (0.2, 1.6 K], not a measured value. Treating the transition temperature as a function of hidden structural and magnetic parameters—effective magnetic thickness, roughness, islanding, interface transparency, exchange scale, and near‐threshold amplification in the Pb layer—we show that several lower‐assumption scenarios reproduce the same above‐floor transport footprint. The strict solitary regime is thus one limiting member of a broader admissible set; isolating it requires characterization transverse to nominal thickness and transport below the present detection floor.