A precursor superconductivity approach to magnetic field effects in the pseudogap phase

Abstract

We study the upper critical field Hc2 (or Tc(H)), and T∗(H) within the pseudogap state, using a mean field scheme which incorporates a strong pairing attraction; for small coupling, g, this approach reduces to BCS theory. However at larger g a pseudogap, Δpg is present at Tc which dramatically changes the behavior of the inferred coherence length ξ, relative to that of BCS theory. Similarly, the quadratic terms in a Ginzburg–Landau description, are modified by Δpg≠0. These pseudogap effects, in accord with experiment, are responsible for the fact that (i) ξ is weakly x-dependent (ii) and Tc is more strongly H dependent than is T∗. Very near the superconductor–insulator transition ξ is predicted to quickly increase.