For a superconductor with a negative curvature in Hc2 Vs T plot we can fit the data by Werthamer–Helfand–Hohenberg (WHH) theory for spin singlet state. For a deviation from the standard spin singlet behaviour one can think of spin triplet behaviour and is confirmed by fitting the data with a p-wave superconductor.

Whereas, for a positive curvature of Hc2(T) near Tc one has to go beyond WHH theory and the feature can be explained by taking into account an effective multi-band model for superconductors. Now how to confirm, whether, the superconducting state is spin singlet (s-wave) or spin triplet (p-wave)?