Microwave surface-impedance measurements of the magnetic penetration depth in single crystal Ba1-xKxFe2As2 superconductors: evidence for a disorder-dependent superfluid density

• Published in: Physical review letters 2009-05, Vol.102 (20), p.207001-207001
• Main Authors: Hashimoto, K, Shibauchi, T, Kasahara, S, Ikada, K, Tonegawa, S, Kato, T, Okazaki, R, van der Beek, C J, Konczykowski, M, Takeya, H, Hirata, K, Terashima, T, Matsuda, Y
• Format: Article
• Language: English
• Subjects: Condensed Matter; Physics; Superconductivity
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.102.207001

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.