Regensburg 2007 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 10: Superconductivity - Properties, Electronic Structure, Order Parameter
TT 10.3: Talk
Tuesday, March 27, 2007, 10:00–10:15, H18
Phonon anomalies in detwinned YBa2Cu3O7−x: Strong ab-anisotropy in the phonon vibrations — •M. Bakr, C. Ulrich, J. Unterhinninghofen, D. Manske, C. Lin, and B. Keimer — Max-Planck-Institute for Solid State Research, Stuttgart, Germany
We have used Raman light scattering to investigate the electronic signal and phonon anomalies in detwinned optimally doped YBa2Cu3O7−x single crystals. Within the experimental error bar, no changes in the electronic gaps was observed with respect to the a and b axes. This is in contrast to previous experimental results observed by ARPES data and Josephson current measurements. All phonons show a pronounced asymmetry, i.e. Fano-profile, which indicates a strong electron-phonon interaction. A pronounced anisotropy in the asymmetry is observed with respect to the crystallographic a and b axes. This anisotropy appears for example for the 340 cm−1 phonon, but the 501 cm−1 phonon shows the largest difference. It is interesting to note that this phonon is right at the energy of the 2 Δmax gap. The anisotropy of the asymmetry parameter, 1/q, is already present in the normal state. Below Tc, the 1/q changes drastically and in a characteristic way for the a and b axes. Finally, we compare our results with Fermi-liquid based calculations. Our results provide further insight into the electron-phonon interaction and therefore the electronic system of high Tc superconductors.