Millimeter-wave surface impedance of optimally-doped Ba(Fe1-xCox)(2)As-2 single crystals

TitleMillimeter-wave surface impedance of optimally-doped Ba(Fe1-xCox)(2)As-2 single crystals
Publication TypeJournal Article
Year of Publication2013
AuthorsBarannik A, Cherpak NT, Tanatar MA, Vitusevich S, Skresanov V, Canfield PC, Prozorov R
Journal TitlePhysical Review B
Date Published01
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberWOS:000313423100004
Keywordshigh-temperature superconductivity, iron, scattering

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)(2)As-2 (x = 0.074, T-c = 22.8 K). Measurements in a millimeter wavelength range (K-a band, 35-40 GHz) were performed using whispering gallery mode excitations in the ultrahigh quality factor quasioptical sapphire disk resonator with YBa2Cu2O7 superconducting (T-c = 90 K) end plates. The temperature variation of the London penetration depth is best described by a power-law function, Lambda lambda(T) similar to T-n, 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, sigma(1)(T), gradually increases with the decrease of temperature, showing no peak below or at T-c, 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 m Omega. DOI: 10.1103/PhysRevB.87.014506

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