Upper critical field of a spin-glass superconductor

Abstract

We have calculated the upper critical magnetic field in a simple-model spin-glass superconductor. We find temperature variations that can deviate significantly from Abrikosov-Gor kov predictions and that strongly reAect the relatively modest underlying temperature dependence of the effective magnetic scattering.

Type II superconductivity

“…9.8 (Fischer, 1978;Newhouse, 1969Newhouse, , p. 1268Vonsovsky et al, 1982, p. 431). Theoretical articles have appeared that discuss upper critical fields (e.g., Brezin et al, 1990;Estrera and Arnold, 1989;Norman, 1990;Perez-Gonzalez and Carbotte, 1992;Perez-Gonzalez et al, 1992;Santhanam and Chi, 1988;Theodorakis and Tesanovic, 1989).…”

Eliashberg Theory of a Multiband Non-Phononic Spin Glass Superconductor

“…In the past papers [13][14][15][16][17][18][19], the developed theory is on phononic superconductors, where it was also added a contribution of antiferromagnetic spin fluctuations (dynamic part) and spin-glass (static part). In this case, it is not necessary to introduce the dynamic part (which is already considered since it is responsible for the pairing of electrons to form Cooper pairs) but only the static part, which is formally equal to the contribution of magnetic impurities with an additional dependence on temperature.…”

“…In this case, it is not necessary to introduce the dynamic part (which is already considered since it is responsible for the pairing of electrons to form Cooper pairs) but only the static part, which is formally equal to the contribution of magnetic impurities with an additional dependence on temperature. The antiferromagnetic spin fluctuations have two components [13][14][15][16][17][18][19]: a dynamical component responsible for s± superconductivity and a static component responsible for the spin-glass behaviour, that goes to zero at spin-glass critical temperature T SG . For T > T SG , the static component disappears and the material behaves like a normal s± superconductor.…”

“…Contribution of the spin-glass phase can be represented in an approximate way in the Eliashberg equations by a term (Γ M (T)) similar to that associated with the presence of magnetic impurities but with a temperature dependence. Precisely, the magnetic impurities scattering rate [16][17][18][19] that mimics the spin-glass state is…”

“…Of course, I do not claim to fully reproduce the complex experimental phenomenology of this material but simply to obtain indications on the relevant input parameters that need to be included in the Eliashberg equations in the hope that one day it will be possible to find a material where only the superconducting state and the spin-glass state appear without any other complications. The starting point will be the theoretical work of M.J. Nass [13][14][15] and J.P Carbotte [16][17][18][19] that describe a single-band spin-glass s-wave phononic superconductor always in the framework of Eliashberg theory.…”