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TT: Fachverband Tiefe Temperaturen

TT 12: Poster Session Superconductivity

TT 12.30: Poster

Montag, 11. März 2013, 15:00–19:00, Poster D

Ultrasonic investigations on the iron-based superconductor Ba(Fe_1−xCo_x)₂As₂ — •Stephan Knöner¹, Bernd Wolf¹, Pham Thanh Cong¹, Thomas Wolf², and Michael Lang¹ — ¹Physikalisches Institut, Goethe-Universität, D-60438 Frankfurt (M) — ²Karlsruhe Institute of Technology, D-76131 Karlsruhe

The simultaneous occurrence of a structural transition and long-range magnetic order in the proximity to the superconducting phase in iron-based superconductors raises the question whether the spin or the lattice degrees of freedom manifest the dominant low-energy excitations in the systems which are relevant for the superconductivity. Based on ultrasonic investigations both scenarios have been discussed in the literature. Ultrasonic experiments on Ba(Fe_1−xCo_x)₂As₂ showed a huge softening of the transverse elastic constant c₆₆ related to the structural tetragonal to orthorhombic/antiferromagnetic phase transition at T_S/T_N and a subsequent hardening upon entering the superconducting state at T_sc. We present measurements of the c₃₃ and 1/2(c₁₁+c₁₂+2c₆₆)-mode together with the ultrasonic attenuation on Ba(Fe_1−xCo_x)₂As₂ single crystals with x=0 and x=0.06. In the undoped compound, two, slightly separated, step-like anomalies of nearly similar size, corresponding to the structural/magnetic transition at T_S/T_N are clearly visible in the c₃₃-mode. According to our characterization measurements by resistivity and susceptibility, our crystal with x=0.06 shows neither a structural nor a magnetic transition but is superconducting at T_sc=24 K. Here the superconducting transition is visible in the c₃₃ as well as in the 1/2(c₁₁+c₁₂+2c₆₆)-mode.