Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: SC: Iron-Based Superconductors - 122

TT 34.7: Talk

Thursday, March 25, 2010, 15:45–16:00, H20

Phonon anomalies in pure and doped R_1−xK_xFe₂As₂ (R=Ba, Sr) investigated by Raman light scattering — •Martin Rahlenbeck¹, Mathieu Le Tacon¹, Guoli Sun¹, Dunlu Sun¹, Chengtian Lin¹, Bernhard Keimer¹, and Clemens Ulrich^1,2,3 — ¹Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany — ²School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia — ³The Bragg Institute, Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales 2234, Australia

We present a detailed temperature dependent Raman light scattering study of optical phonons in superconducting and non-superconducting R_1−xK_xFe₂As₂ (R=Ba, Sr) single crystals. In all samples we observe a strong continuous narrowing of the Raman-active Fe and As vibrations upon cooling below the spin-density-wave transition T_s. We attribute this effect to the opening of the spin-density-wave gap. The electron-phonon linewidths inferred from these data greatly exceed the predictions of ab-initio density functional calculations without spin polarization, which may imply that local magnetic moments survive well above T_s. A first-order structural transition accompanying the spin-density-wave transition induces discontinuous jumps in the phonon frequencies. These anomalies are increasingly suppressed for higher potassium concentrations. We also observe a pronounced splitting of the E_g modes at this transition temperature. At the superconducting transition temperature T_c we observe subtle phonon anomalies with a behavior qualitatively similar to that in the cuprate superconductors.