Effects of heavy-ion irradiation on the microwave surface impedance of (Ba1−xKx)Fe2As2 single crystals

• Published in: Superconductor science & technology 2018-02, Vol.31 (3)
• Main Authors: Ghigo, G, Torsello, D, Gerbaldo, R, Gozzelino, L, Laviano, F, Tamegai, T
• Format: Article
• Language: English
• Subjects: heavy-ion irradiation; iron-based superconductors; microwave surface impedance
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/1361-6668/aaa858

The electrodynamic response of Ba1−xKxFe2As2 single crystals at the microwave frequencies has been investigated by means of a coplanar resonator technique, at different values of non-magnetic disorder introduced into the samples by heavy-ion irradiation. The surface impedance Zs = Rs + iXs conforms to the classical skin effect above the critical temperature. Below Tc, Rs monotonically decreases while Xs shows a peak, which evolves as a function of the irradiation fluence. The disorder-dependent Zs(T) curves are analyzed within a two-fluid model, suitably modified to account for a finite quasiparticle fraction at T = 0. The analysis gives, for the unirradiated crystal, quasiparticle relaxation times τ that are in good agreement with previous literature. Smaller τ values are deduced for the disordered crystals, both in the normal and in the superconducting states. The limits of application of the model are discussed.