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

Abstract

The crystal structure and lattice phonons of (BEDT-TTF)_2I_3 superconducting β-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 λis found to be around 0.4 .

arXiv comment15 pages, 5 figures, RevTeX 3.1 - Replacement for cond-mat 0003297 We have corrected Section IIE, where the analytical average over the Fermi surface was incorrect. We performed the average numerically over the Fermi surface generated by our dimer model. The λvalue is practically unchanged

References in corpus (3)

• kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br: a Fully Gapped Strong-Coupling Superconductor
• Cyclotron effective masses in layered metals
• The Dimer Model for k-phase Organic Superconductors

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