Thomsen C., Cardona M., Friedl B., Rodriguez C.O., Mazin I.I., Andersen O.K.
The authors report quantitative evidence from Raman scattering for the applicability of strong-coupling theory for phonon self-energies to high-Tc superconductors. Positive and negative shifts of optical phonon frequencies in the superconducting state of RBa2Cu3O74-delta fall near a universal curve when plotted vs. phonon energy. This curve is the phonon self-energy shift obtained from strong-coupling theory by Zeyher and Zwicknagl, with 2 Delta /kBTc=5.2. The appropriate electron-phonon coupling constants ( lambda =0.02 and 0.01 for the 340 and 440-cm-1 modes) were calculated ab initio.
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