title: Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor.
abstract: There are two prerequisites for understanding high-temperature (high-Tc) superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges. The nature of the normal state of iron-pnictide superconductors, and the role played by correlations arising from partially screened interactions, are still under debate. Here we show that the normal state of carefully annealed electron-doped BaFe(2-x)Co(x)As2 at low temperatures has all the hallmark properties of a local Fermi liquid, with a more incoherent state emerging at elevated temperatures, an identification made possible using bulk-sensitive optical spectroscopy with high frequency and temperature resolution. The frequency dependent scattering rate extracted from the optical conductivity deviates from the expected scaling M2 (ω, T) ∝ (ħω)(2) + (pπkBT)(2) with p ≈ 1.47 rather than p = 2, indicative of the presence of residual elastic resonant scattering. Excellent agreement between the experimental results and theoretical modeling allows us to extract the characteristic Fermi liquid scale T0 ≈ 1700 K. Our results show that the electron-doped iron-pnictides should be regarded as weakly correlated Fermi liquids with a weak mass enhancement resulting from residual electron-electron scattering from thermally excited quasi-particles.
authors.affiliation: van der Waals-Zeeman institute, University of Amsterdam Amsterdam XL, 1098 XH, The Netherlands.
authors.forename: Alona
authors.initials: A
authors.lastname: Tytarenko
authors.affiliation: van der Waals-Zeeman institute, University of Amsterdam Amsterdam XL, 1098 XH, The Netherlands.
authors.forename: Yingkai
authors.initials: Y
authors.lastname: Huang
authors.affiliation: van der Waals-Zeeman institute, University of Amsterdam Amsterdam XL, 1098 XH, The Netherlands.
authors.forename: Anne
authors.initials: A
authors.lastname: de Visser
authors.affiliation: Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Johnston
authors.affiliation: van der Waals-Zeeman institute, University of Amsterdam Amsterdam XL, 1098 XH, The Netherlands.
authors.forename: Erik
authors.initials: E
authors.lastname: van Heumen