Penetration depth and flux-flow resistivity measurements of BaFe2(As0.55P0.45)2 single crystals

Abstract

We measured the surface impedance of BaFe2(As0.55P0.45)2 single crystals under finite magnetic fields by using a microwave technique. We found that the penetration depth increased as λ(T)=λ(0)+A×Tn with an exponent of n≈1.7 in the temperature region of 0.1<T/Tc<0.2. The observed fractional exponent can be understood by considering that this material has gaps with lines of nodes and nodeless gaps with large anisotropy. The flux-flow resistivity showed an almost H-linear dependence and a remarkably rapid enhancement in the low-H region; ρf/ρn≈αH/Hc2 with a gradient of α>2.5. Such a behavior is similar to that of SrFe2(As,P)2. By comparing these with results of 111-materials and SrFe2(As0.7P0.3)2, it has been clarified that the gap anisotropy dominates the gradient α of iron-based materials.