Effects of the order parameter symmetry on the vortex core structure in the iron pnictides

Abstract

Effects of the order parameter symmetry on the cutoff parameter ξh (determining the magnetic field distribution) in the mixed state are investigated in framework of quasiclassical Eilenberger theory for isotropic s± and for s++ pairing symmetries of superconductors using computational methods. In s± pairing symmetry the gap function has opposite sign and equal absolute values of the electron and hole pockets of the Fermi surface and in s++ pairing symmetry the gap function has the same sign of the electron and hole pockets of the Fermi surfaces. The s± pairing symmetry results in different effects of intraband (Γ0) and interband (Γπ) impurity scattering on ξh. It is found that ξh/ξc2 decreases with the Γ0 leading to values much less than those predicted by the analytical Ginzburg-Landau (AGL) theory for high Γ0. At very high Γ0 the interband scattering suppresses ξh/ξc2 considerably less than the one in the whole field range making it flat. If Γ0 and Γπ are small and equal then the ξh/ξc2(B/Bc2) dependence behaves like that of the AGL model and shows a minimum with value much more than that obtained for s++ superconductors. With high Γπ the dependence of ξh/ξc2(B/Bc2) resides above the AGL curve. Such behavior is quite different from that in s++ pairing symmetry where intraband and interband scattering rates act in a similar way and ξh/ξc2 decreases monotonously with impurity scattering and resides below the AGL curve.