Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 17: Superconductivity: Fe-based Superconductors - 122 Part 2 & Theory

TT 17.3: Vortrag

Dienstag, 27. März 2012, 10:00–10:15, H 2053

Signatures of non-Fermi liquid behavior in hole-doped and chemically pressurized EuFe₂As₂ single crystals — •Jeevan .s Hirale, Jannis Maiwald, and Philipp Gegenwart — I. Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich Hund Platz 1, 37077 Göttingen, Germany

We report a detailed study of the effect of hole-doping and chemical pressure (isovalent doping) in single crystals of K_xEu_1−xFe₂As₂ and EuFe₂(As_1−yP_y)₂, respectively, by measurements of the thermopower, S(T), and electrical resistivity, ρ(T). In this class of FeAs-based superconductivity (SC), it is found that SC appears close to a magnetic instability, suggesting a possible unconventional pairing mechanism. We have synthesized single crystals of both K and P doped samples by the self-flux method. Upon doping Eu with K >30%, T_SDW gets suppressed and SC appears with T_c,max≈34 K. Additionally, the Eu²⁺ ordering is suppressed to low temperatures, due to the dilution of magnetic moments. On the other hand, P doping the As site suppresses the SDW transition and results in a SC phase at y>16%. The electrical resistivity data suggest non-Fermi liquid behavior near x=0.5 and y=0.2 . This is supported by the observation of a logarithmic divergence in the thermoelectric power coefficient S/T for both systems. We also observe distinct signatures in the thermopower evolution at x_cr=0.30 and y_cr=0.22, which may hint at Lifshitz transitions of the Fermi surface.

Work supported by DFG through priority program SPP 1458.