Electron-Phonon Coupling Deduced from Phonon Line Shapes

• Published in: physica status solidi (b) Vol. 215; no. 1; pp. 495 - 500
• Main Authors: Bock, A., Ostertun, S., Subke, K.-O.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01.09.1999; WILEY‐VCH Verlag
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/(SICI)1521-3951(199909)215:1<495::AID-PSSB495>3.0.CO;2-X

We investigate the Fano‐type line shape of the Ba mode of Y1—xCaxBa2Cu3O6+y films observed in Raman spectra with A1g symmetry. The line shape is described with an extended Fano formula that allows us to obtain the bare phonon parameters and the self‐energy effects based on a phenomenological description of the real and imaginary part of the low‐energy electronic response. It turns out that the phonon intensity originates almost entirely from a coupling to this electronic response with negligible contributions from interband (high‐energy) electronic excitations. In the normal state we obtain a measure of the electron–phonon coupling via the mass‐enhancement factor λ. We find λ‐ = 6.8 ± 0.5% around optimum doping and only weak changes of the self‐energy in the superconducting state. With increased disorder at the Ba site we find a decreased intensity of the Ba mode which we can relate to a decreased electron–phonon coupling.