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.