Cutoff parameter and vortex core size ind-wave superconductors

P Belova,A Sharafeev,I Zakharchuk,K B Traito,E Lähderanta

doi:10.1051/epjconf/20147507002

Abstract

There is some evidence that the electron-phonon mechanism is not strong enough to produce ob- served 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 pa- rameter 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 super- conductors: 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 =Φ 0/2πξc2 2 . The ξ2/ξc2(B/Bc2) dependence is monotonously decreasing function at intermediate and high temperatures.

Highlights

A nontrivial orbital structure of the order parameter, in particular the presence of the gap nodes, leads to an effect in which the disorder is much richer in dx2−y2 -wave superconductors than in conventional materials
A finite concentration of disorder produces a nonzero density of quasiparticle states at zero energy, which results in a considerable modification of the thermodynamic and transport properties at low temperatures
Eilenberger equations have been solved for superconductors with dx2−y2 pairing symmetry in the mixed state

Summary

Introduction

A nontrivial orbital structure of the order parameter, in particular the presence of the gap nodes, leads to an effect in which the disorder is much richer in dx2−y2 -wave superconductors than in conventional materials. A finite concentration of disorder produces a nonzero density of quasiparticle states at zero energy, which results in a considerable modification of the thermodynamic and transport properties at low temperatures. For a pure superconductor in a d-wave-like state at temperatures T well below the critical temperature Tc, the deviation Δλ of the penetration depth from its zero-temperature value λ(0) is proportional to T. Unlike s-wave superconductor, impurity scattering suppresses both the transition temperature Tc and the upper critical field Hc2(T ) [9]

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Conclusion