Limits of the upper critical field in dirty two-gap superconductors

Abstract

An overview of the theory of the upper critical field in dirty two-gap superconductors, with a particular emphasis on MgB2 is given. We focus here on the maximum Hc2 which may be achieved by increasing intraband scattering, and on the limitations imposed by weak interband scattering and paramagnetic effects. In particular, we discuss recent experiments which have recently demonstrated ten-fold increase of Hc2 in dirty carbon-doped films as compared to single crystals, so that the Hc2(0) parallel to the ab planes may approach the BCS paramagnetic limit, Hp[T ] = 1.84Tc[K] ≃ 60 − 70T . New effects produced by weak interband scattering in the two-gap Ginzburg-Landau equations and Hc2(T ) in ultrathin MgB2 films are addressed.

Comparative photoemission studies on the superconducting gap of the filled skutterudite superconductors LaPt4Ge12and PrPt4Nakamura1, Okazaki2, Yoshida3 et al. 2012Phys. Rev. B246221View full textAdd to dashboardCite

“…23 Existence of multiband crossings or multiple Fermi surface sheets are a condition for multigap superconductivity. An upturn of the upper critical field as a function of temperature for the higher T c region, one of the characteristics of two-gap superconductivity, 24,25 is indeed observed in PrPt 4 Ge 12 . Improvement of energy resolution may help to distinguish full details of superconducting gap structure.…”

Pressure-induced superconductivity in the three-dimensional topological Dirac semimetal Cd3As2

“…The linear temperature dependence of H c2 in Figure 3b is actually very interesting. It may come from a two-band Fermi surface topology as in MgB 2 , [35][36][37] or an unconventional superconducting state as in heavy-fermion compound UBe 13 . 38 11,[39][40][41] We notice that no superconductivity was observed up to 13.43 GPa in an earlier pressure study of Cd 3 As 2 single crystal.…”

Low anisotropy of the upper critical field in a strongly anisotropic layered cuprateBi2.15Sr1.9CuO6+δ:Evidence for a paramagnetically limited superconductivity

“…It is particularly important for understanding unconventional superconductivity [2,3]. However, estimation of H c2 for high-temperature superconductors is a notoriously difficult task.…”