Physics and Astronomy, Ames Laboratory
Journal or Book Title
Physical Review B
Precision measurements of active and reactive components of in-plane microwave surface impedance were performed in single crystals of optimally-doped Fe-based superconductor Ba(Fe1−xCox)2As2 (x=0.074, Tc=22.8 K). Measurements in a millimeter wavelength range (Ka band, 35–40 GHz) were performed using whispering gallery mode excitations in the ultrahigh quality factor quasioptical sapphire disk resonator with YBa2Cu2O7 superconducting (Tc=90 K) end plates. The temperature variation of the London penetration depth is best described by a power-law function, Δλ(T)∼Tn, n=2.8, in reasonable agreement with radio-frequency measurements on crystals of the same batch. This power-law dependence is characteristic of a nodeless superconducting gap in the extended s-wave pairing scenario with a strong pair-breaking scattering. The quasiparticle conductivity of the samples, σ1(T), gradually increases with the decrease of temperature, showing no peak below or at Tc, in notable contrast with the behavior found in the cuprates. The temperature-dependent quasiparticle scattering rate was analyzed in a two-fluid model, assuming the validity of the Drude description of conductivity and generalized expression for the scattering rate. This analysis allows us to estimate the range of the values of a residual surface resistance from 3 to 6 mΩ.
American Physical Society
Barannik, A.; Cherpak, N. T.; Skresanov, V.; Tanatar, Makariy A.; Vitusevich, S.; Canfield, Paul C.; and Prozorov, Ruslan, "Millimeter-wave surface impedance of optimally-doped Ba(Fe1-xCox)(2)As-2 single crystals" (2013). Physics and Astronomy Publications. 624.