Superconducting-Gap Anisotropy of Iron Pnictides Investigated via Combinatorial Microwave Measurements

Abstract

AbstractOne of the most significant issues for superconductivity is clarifying the momentum-dependent superconducting gap Δ($${\boldsymbol{k}}$$k), which is closely related to the pairing mechanism. To elucidate the gap structure, it is essential to investigate Δ($${\boldsymbol{k}}$$k) in as many different physical quantities as possible and to crosscheck the results obtained in different methods with each other. In this paper, we report a combinatorial investigation of the superfluid density and the flux-flow resistivity of iron-pnictide superconductors; LiFeAs and BaFe2(As1−xPx)2 (x = 0.3, 0.45). We evaluated Δ($${\boldsymbol{k}}$$k) by fitting these two-independent quantities with a two-band model simultaneously. The obtained Δ($${\boldsymbol{k}}$$k) are consistent with the results observed in angle-resolved photoemission spectroscopy (ARPES) and scanning-tunneling spectroscopy (STS) studies. We believe our approach is a powerful method for investigating Δ($${\boldsymbol{k}}$$k) because it does not require a sample with clean surface unlike ARPES and STS experiments, or a rotational magnetic-field system for direct measurements of the angular dependence of thermodynamic quantities.