2011/12/05 by V. G. Kogan, R. Prozorov, Kogan, V. G. +1
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity (cond-mat.supr-con) #Superconductivity in MgB2 and Alloys
paper · pdf · doi:10.48550/arxiv.1112.0996
openalex publication_date 2011/12/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The Helfand-Werthamer (HW) scheme\citeHW of evaluating the orbital upper critical field is generalized to anisotropic superconductors in general, and to two-band clean materials, in particular. Our formal procedure differs from those in the literature; it reproduces not only the isotropic HW limit, but also the results of calculations for the two-band superconducting MgB2\citeMMK,DS along with the existing data on Hc2(T) and its anisotropy γ(T)=Hc2,ab(T)/Hc2,c(T) (a,c are the principal directions of a uniaxial crystal). Using rotational ellipsoids as model Fermi surfaces we apply the formalism developed to study γ(T) for a few different anisotropies of the Fermi surface and of the order parameters. We find that even for a single band d-wave order parameter γ(T) decreases on warming, however, relatively weakly. For order parameters of the form Δ(kz) = Δ0(1+ηcos kza),\citeXu according to our simulations γ(T) may either increase or decrease on warming even for a single band depending on the sign of η. Hence, the common belief that the multi-band Fermi surface is responsible for the temperature variation of γ is proven incorrect.