Cutoff parameter and vortex core size in d-wave superconductors

¹ Lappeenranta University of Technology, P.O. Box 20, FI-53851, Lappeenranta, Finland
² Petrozavodsk State University, Lenin str. 33, RU-185640, Petrozavodsk, Russia
³ Saint-Petersburg Electrotechnical University, Popovstr.5, RU-197376, St.Petersburg, Russia

^a e-mail: polina.belova@lut.fi

Published online: 3 July 2014

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 T_c = 3 K and high-T_c cuprates. In this work the Eilenberger equations are solved for anisotropic d_x²−_y²-wave superconductors. The cutoff parameter ξ_h 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 ξ_h/ξ_c2 in d_x²−_y²-wave superconductors are similar to those in s-wave superconductors: ξ_h/ξ_c2(B/B_c2)dependence has minimum at high temperatures and shows monotonously increasing behavior at low temperatures. Here, ξ_c2 is determined by the relation B_c2 =Φ₀/2πξ_c2². The ξ₂/ξ_c2(B/B_c2) dependence is monotonously decreasing function at intermediate and high temperatures.