Millimeter-wave study of London penetration depth temperature dependence in Ba(Fe0.926Co0.074)2As2 single crystal

Abstract

In-plane surface Ka-band microwave impedance of optimally doped single crystals of the Fe-based superconductor Ba(Fe0.926Co0.074)2As2 (Tc= 22.8K) was measured. Sensitive sapphire disk quasi-optical resonator with high-Tc cuprate conducting endplates was developed specially for Fe-pnictide superconductors. It allowed finding temperature variation of London penetration depth in a form of power law, namely Δλ(T)~ Tn with n = 2.8 from low temperatures up to at least 0.6Tc consisted with radio-frequency measurements. This exponent points towards nodeless state with pairbreaking scattering, which can support one of the extended s-pairing symmetries. The dependence λ(T) at low temperatures is well described by one superconducting small-gap (Δ\cong 0.75 in kTc units, where k is Boltzman coefficient) exponential dependence.

6 pages, 2 figures, to be published in Low Temperature Physics,vol.37, August 2011

References in corpus (9)

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• Superfluid density in the $s_{\pm }$-wave state of clean iron-based superconductors
• On the determination of the quasiparticle scattering rate in unconventional superconductors by microwave surface impedance