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Lattice dynamics and electron-phonon coupling in \beta-(BEDT-TTF)_2I_3 organic superconductor

A. Girlando·M. Masino·G. Visentini·R. G. Della Valle·A. Brillante·E. Venuti
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Abstract

The crystal structure and lattice phonons of (BEDT-TTF)_2I_3 superconducting \beta-phase are computed and analyzed by the Quasi Harmonic Lattice Dynamics (QHLD) method. Whereas the crystal structure and its temperature and pressure dependence are properly reproduced within a rigid molecule approximation, this has to be removed to account for the specific heat data. Such a mixing between lattice and low-frequency intramolecular vibrations also yields good agreement with the observed Raman and infrared frequencies. From the eigenvectors of the low-frequency phonons we calculate the electron-phonon coupling constants due to the modulation of charge transfer (hopping) integrals. The hopping integrals are evaluated by the extended Hueckel method applied to all nearest-neighbor BEDT-TTF pairs in the ab crystal plane. From the averaged electron-phonon coupling constants and the QHLD phonon density of states we derive the Eliashberg coupling function, which compares well with that experimentally obtained from point-contact spectroscopy. The corresponding dimensionless coupling constant \lambda is found to be around 0.4 .

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A. Girlando, M. Masino, G. Visentini, R. G. Della Valle, A. Brillante, E. Venuti. 2000-03-17. Lattice dynamics and electron-phonon coupling in \beta-(BEDT-TTF)_2I_3 organic superconductor. https://doi.org/10.1103/physrevb.62.14476

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