The orbital upper critical field Hc2 is evaluated for isotropic materials with arbitrary transport and pair-breaking scattering rates. It is shown that unlike transport scattering which enhances Hc2, the pair breaking suppresses the upper critical field and reduces the dimensionless ratio h∗(0)=Hc2(0)/Tc(dHc2/dT)Tc from the Helfand-Werthamer value of ≈0.7 to 0.5 for a strong pair-breaking. h∗(T) is evaluated for arbitrary transport and pair-breaking scattering. A phenomenological model for the pair-breaking suppression by magnetic fields is introduced. It shows qualitative features such as a positive curvature of Hc2(T) and the low temperature upturn usually associated with multi-band superconductivity.
@article{arxiv.1305.6030,
title = {Orbital upper critical field of type-II superconductors with pair breaking},
author = {V. G. Kogan and R. Prozorov},
journal= {arXiv preprint arXiv:1305.6030},
year = {2013}
}