Dresden 2011 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 36: SC: Fe-based Superconductors - 122 - Properties, Electronic Structure, Mechanisms

TT 36.4: Vortrag

Mittwoch, 16. März 2011, 14:45–15:00, HSZ 304

Doping dependent electronic anisotropies in Ba(Fe_1−xCo_x)₂As₂ — •F. Kretzschmar¹, B. Muschler¹, R. Hackl¹, J.-H. Chu^{2, 3}, J. G. Analytis^2,3, and I. R. Fisher^{2, 3} — ¹Walther Meissner Institute, 85748 Garching — ²SIMES, SLAC, Menlo Park, CA 94025, USA — ³GLAM, Stanford University, CA 94305, USA

Superconductivity in the iron pnictides with T_c up to 56 K does probably not originate from electron-phonon coupling. The compounds have well nested hole and electron pockets with similar cross sections encircling the (π,0) points and the center of the (1 Fe) unit cell which can essentially be probed independently by electronic Raman scattering (ERS) in A_1g and B_1g symmetry, respectively. We present results of ERS experiments on Ba(Fe_1−xCo_x)₂As₂ measured as a function of temperature, T>T_c, and doping x. The data of five samples with x=0.045, 0.051, 0.055, 0.061, and 0.085 with T_c^max=24 K at x=0.061 were analyzed applying an extended Drude model. The resulting dynamical relaxation rates Γ_µ(ω,T) are distinctly different in the two symmetries µ. In particular, the zero-energy extrapolation values Γ_µ(ω → 0,T) vary strongly for B_1g and weakly for A_1g symmetry indicating a band dependence of the electronic relaxation. Surprisingly, (Γ_A1g+Γ_B1g)/2 compares well with the temperature dependence of the DC resistivity. The anisotropy resembles that in cuprates. However, in the cuprates the electronic relaxation depends on the location on a single Fermi surface rather than on the individual sheet. We conclude, that in either case only the coupling of the electrons to spin and/or charge excitations can explain these anisotropies.