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

•We measure surface impedances of BaFe2(As0.55P0.45)2 under finite magnetic fields.•The penetration depth indicates the presence of highly anisotropic gap structures.•Rapid enhancement of the flux-flow resistivity supports highly anisotropic gaps.

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×Tnλ(T)=λ(0)+A×Tn with an exponent of n≈1.7n≈1.7 in the temperature region of 0.12.5α>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 αα of iron-based materials.