Vortex core size in unconventional superconductors

Abstract

Influence of the order parameter symmetries on the cutoff parameter ξh and vortex core size ξ2 (the distance from the vortex center at which the current density reaches the maximum value) in the mixed state are investigated in the framework of Eilenberger theory for unconventional superconductors. The cutoff parameter determines the field distribution in the generalized London equation obtained as a projection of the quasiclassical theory. It is used for the fitting of the μSR and small-angle neutron scattering experimental data. Anisotropic dx2−y2 and isotropic s±-wave superconducting pairings are studied. These pairing symmetries can be realized in iron pnictide superconductors. Conventional s++ pairing mediated electron-phonon interaction is also considered. Temperature, field, and impurity scattering dependences of ξh/ξc2 are obtained. It is found that normalized ξ2/ξc2(B/Bc2) dependence is increasing with pair breaking impurity scattering (interband scattering for s±-wave and intraband impurity scattering for d-wave superconductors). Here, ξc2 is the Ginzburg-Landau coherence length determined from the relation Bc2=Φ0/2πξc22, where Bc2 is an upper critical field and Φ0 is a flux quantum. Two types of ξ2/ξc2(B/Bc2) dependences are obtained for s± superconductors. It has minimum at low temperatures and small impurity scattering transforming in monotonously decreasing function at strong scattering and high temperatures. The second kind of this dependence was also found for d-wave superconductors at intermediate and high temperatures. In contrast, impurity scattering results in decreasing of ξ2/ξc2 field dependence in s++ superconductors.