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Precision Microwave Electrodynamic Measurements of K- and Co-doped BaFe$_2$As$_2$ | | J. S. Bobowski
; J. C. Baglo
; James Day
; P. Dosanjh
; Rinat Ofer
; B. J. Ramshaw
; Ruixing Liang
; D. A. Bonn
; W. N. Hardy
; Huiqian Luo
; Zhao-Sheng Wang
; Lei Fang
; Hai-Hu Wen
; | | Date: |
20 Sep 2010 | | Abstract: | We have studied the microwave electrodynamics of single crystal iron-based
superconductors Ba$_{0.72}$K$_{0.28}$Fe$_2$As$_2$ (hole-doped,
$T_mathrm{c}$~$approx~$30~K) and Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$
(electron-doped, $T_mathrm{c}$~$approx$20~K), by cavity perturbation and
broadband spectroscopy. SQUID magnetometry was used to confirm the quality and
homogeneity of the samples under study. Through cavity perturbation techniques,
the temperature dependence of the in-plane London penetration depth
$Deltalambda(T)$, and therefore the superfluid phase stiffness
$lambda^2(0)$/$lambda^2(T)$ was measured. Down to 0.4~K, the data do not show
the exponential saturation at low temperatures expected from a singly-,
fully-gapped superconductor. Rather, both the electron- and the hole-doped
systems seem to be best described by a power law behavior, with
$lambda^2(0)$/$lambda^2(T)$~$sim$~$T^n$ and emph{n}~$approx$~2.5. In the
three samples we studied, a weak feature near the sensitivity limit of our
measurements appears near $T/T_mathrm{c}$~=~0.04, hinting at a corresponding
low energy feature in the superconducting density of states. The data can also
be relatively well-described by a simple two-gap $s$-wave model of the order
parameter, but this yields parameters which seem unrealistic and dependent on
the fit range. Broadband surface resistance measurements reveal a sample
dependent residual loss whose origin is unclear. The data from the
FeAs~samples can be made to scale as~$omega^2$ if the extrinsic loss is
treated as an additive component, indicating large scattering rates. Finally,
the temperature dependence of the surface resistance at 13~GHz obeys a power
law very similar to those observed for $Deltalambda(T)$. | | Source: | arXiv, 1009.3941 | | Services: | Forum | Review | PDF | Favorites | |
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