Temperature dependent phonon mode coupling in YBCO_6.95
Abstract
While the majority in the field of high-temperature superconductivity believe in the magnetic mechanism, experimental evidence of phonon involvement is increasing. We carried out inelastic neutron scattering measurements of c-axis phonons with a YBa_2Cu_3O_6.95 single crystal at the MAPS of the ISIS facility. We found distinct temperature dependence of the 63 meV apical oxygen phonon mode, which correlates well with that of the in-plane Cu-O bond-stretching phonon mode observed earlier. The result indicates that the coupling between the two modes changes with temperature, similar to the superconducting order parameter. The coupling is mainly due to the Coulomb repulsion between the in-plane oxygen and the apical oxygen. The phonon-induced hole transfer from oxygen to copper introduces attractive force and offsets this repulsion. The observed effect can be explained by the enhancement of offset due to the off-diagonal transfer of Cooper pairs. Thus this observation constitutes the direct confirmation of involvement of the in-plane Cu-O bond-stretching phonons in the superconductivity of YBCO_6.95.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARJ12009S