Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 27: Superconductivity: Fe-based Superconductors - 122
TT 27.4: Talk
Tuesday, March 12, 2013, 10:30–10:45, H18
Raman active phonons in twin-free BaFe2As2 — •Andreas Baum1, Bernhard Muschler1, Florian Kretzschmar1, Jiun-Haw Chu2,3, James G. Analytis2,3, Ian R. Fisher2,3, 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 Eg vibration of the Fe and As atoms at 135 cm−1 splits into a B2g and a B3g mode at 138 and 128 cm−1, respectively, below the SDW transition. The unexpected leakage of the As A1g phonon observed in the tetragonal B2g 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.