TUESDAY, Mar. 1, 12 p.m. 11 FLOOR OF THE GAMOW TOWER
Dmitry Reznik
Neutron Scattering Group
Forschungszentrum Karlsruhe
Institut für Festkörperphysik, Germany
Electron phonon coupling in solids with complex interactions.
Conventional theory of electron-phonon coupling is extremely powerful in explaining many properties of charge-density-wave (CDW) systems as well as conventional superconductors. Theory and experiment both show that phonon-mediated high temperature superconductivity occurs in compounds where a tendency to a CDW instability competes with superconductivity. These systems involve exceptionally strong coupling of electronic excitations to particular phonons, hich can be predicted by band theory. MgB2 and YNi2B2C are good examples of such superconductors. Recent neutron and x-ray scattering experiments revealed that the phenomenology of electron-phonon coupling in solids with complex interactions is surprisingly similar although band theory cannot explain these effects. For example, strong phonon softening was found in copper oxide superconductors, which may be related to dynamic stripe formation but completely unexpected from band theory. A similar effect has been observed in a CMR manganite, although here the phonon anomaly is phenomenologically associated with short range charge order that appears above the ferromagnetic transition temperature.