Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...
TT 18.8: Vortrag
Dienstag, 28. März 2006, 17:00–17:15, HSZ 02
Strong electron-phonon coupling in YNi2B2C: Theory and Experiment — •F. Weber1,2, A. Kreyssig3, L. Pintschovius1, K. Hradil4, K.-P. Bohnen1, R. Heid1, and W. Reichardt1 — 1Forschungszentrum Karlsruhe, Inst. f. Festkörperphysik — 2Fak. f. Physik, Univ. Karlsruhe — 3IAPD, TU Dresden — 4PCI, Univ. Göttingen
Several compounds of the family RENi2B2C (RE=Y, Lanthanoid) exhibit high superconducting transition temperatures (up to about 20 K) which is thought to be due to strong electron-phonon coupling (EPC). We made extensive calculations using density functional theory which indeed predict an EPC strength sufficient to explain the observed Tc’s. We note that the strong EPC gives rise to pronounced anomalies in the phonon dispersion curves and concurrently to large line widths of certain phonon modes. In particular, there should be a pronounced phonon anomaly at the zone boundary in the (110)-direction (the so-called M-point) in addition to the already known anomaly in the (100)-direction. Inelastic neutron scattering measurements were performed on YNi2B2C on the triple axis spectrometer PUMA, Munich. The data show an extremely good agreement between the predicted and the observed phonon frequencies. Moreover, the measurements confirm the strong line broadening of the anomalous M-point mode predicted by theory. Finally, measurements in different Brillouin zones confirm the theoretical predictions, that in spite of the low frequency of the anomalous mode its eigenvector contains rather large amplitudes of the light atoms B and C.