title: Microwave surface-impedance measurements of the magnetic penetration depth in single crystal Ba1-xKxFe2As2 superconductors: evidence for a disorder-dependent superfluid density.
abstract: We report high-sensitivity microwave measurements of the in-plane penetration depth lambda_{ab} and quasiparticle scattering rate 1/tau in several single crystals of the hole-doped Fe-based superconductor Ba(1-x)K(x)Fe(2)As(2) (x approximately 0.55). While a power-law temperature dependence of lambda_{ab} with a power approximately 2 is found in crystals with large 1/tau, we observe an exponential temperature dependence of the superfluid density consistent with the existence of fully opened two gaps in the cleanest crystal we studied. The difference may be a consequence of different levels of disorder inherent in the crystals. We also find a linear relation between the low-temperature scattering rate and the density of quasiparticles, which shows a clear contrast to the case of d-wave cuprate superconductors with nodes in the gap. These results demonstrate intrinsically nodeless order parameters in the Fe arsenides.
authors.affiliation: Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hashimoto
authors.forename: T
authors.initials: T
authors.lastname: Shibauchi
authors.forename: S
authors.initials: S
authors.lastname: Kasahara
authors.forename: K
authors.initials: K
authors.lastname: Ikada
authors.forename: S
authors.initials: S
authors.lastname: Tonegawa
authors.forename: T
authors.initials: T
authors.lastname: Kato
authors.forename: R
authors.initials: R
authors.lastname: Okazaki
authors.forename: C J
authors.initials: CJ
authors.lastname: van der Beek
authors.forename: M
authors.initials: M
authors.lastname: Konczykowski
authors.forename: H
authors.initials: H
authors.lastname: Takeya
authors.forename: K
authors.initials: K
authors.lastname: Hirata
authors.forename: T
authors.initials: T
authors.lastname: Terashima
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuda