Cutoff parameter and vortex core size in d-wave superconductors

Abstract

There is some evidence that the electron-phonon mechanism is not strong enough to produce observed high critical temperatures in unconventional superconductors; this is the case in both the cuprates and Fe-based superconductors. The d-wave pairing in strongly correlated systems is consistent with the observation of nodal quasiparticles in the heavily hole doped superconductor KFe2As2 with Tc = 3 K and high-Tc cuprates. In this work the Eilenberger equations are solved for anisotropic dx2−y2-wave superconductors. The cutoff parameter ξh and vortex core size ξ2 (the distance from the vortex center to the radius where the current density reaches its maximum value) in the mixed state are investigated numerically. The cutoff parameter determines the field distribution in the generalized London equation obtained as a projection of the quasiclassical theory. It can be used for the fitting of the µSR and small-angle neutron scattering (SANS) experimental data. Field and temperature dependences of ξh/ξc2 in dx2−y2-wave superconductors are similar to those in s-wave superconductors: ξh/ξc2(B/Bc2)dependence has minimum at high temperatures and shows monotonously increasing behavior at low temperatures. Here, ξc2 is determined by the relation Bc2 =Φ0/2πξc22. The ξ2/ξc2(B/Bc2) dependence is monotonously decreasing function at intermediate and high temperatures.