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TT: Fachverband Tiefe Temperaturen

TT 27: Superconductivity: Fe-based Superconductors - 122

TT 27.4: Vortrag

Dienstag, 12. März 2013, 10:30–10:45, H18

Raman active phonons in twin-free BaFe₂As₂ — •Andreas Baum¹, Bernhard Muschler¹, Florian Kretzschmar¹, Jiun-Haw Chu^2,3, James G. Analytis^2,3, Ian R. Fisher^2,3, and Rudi Hackl¹ — ¹Walther-Meissner-Institut, 85748 Garching, Germany — ²SIMES, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA — ³GLAM and Department of Applied Physics, Stanford University, Stanford, CA 94305, USA

The magneto-structural phase transition of BaFe₂As₂ is studied by Raman spectroscopy. The main focus is placed on the anomalies of the lattice dynamics upon entering the spin density wave (SDW) phase. Since the related lattice distortion is very small the crystals are twinned, and in the existing experiments the properties of the phonons could only partially be clarified. To overcome the problem of twinning uniaxial stress was applied before cool down. In the twin-free crystals the symmetry properties of the phonons could be pinned down. The E_g vibration of the Fe and As atoms at 135 cm⁻¹ splits into a B_2g and a B_3g mode at 138 and 128 cm⁻¹, respectively, below the SDW transition. The unexpected leakage of the As A_1g phonon observed in the tetragonal B_2g symmetry can be traced back to a resonance effect occuring only when the incoming and outgoing photon polarizations are oriented parallel to the new orthorhombic b axis along which the Fe spins order ferromagnetically.