Microwave surface-impedance measurements of the magnetic penetration depth in single crystal Ba1-xKxFe2As2 superconductors: evidence for a disorder-dependent superfluid density.
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.
Hashimoto
K
K
Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Shibauchi
T
T
Kasahara
S
S
Ikada
K
K
Tonegawa
S
S
Kato
T
T
Okazaki
R
R
van der Beek
C J
CJ
Konczykowski
M
M
Takeya
H
H
Hirata
K
K
Terashima
T
T
Matsuda
Y
Y