Phonon self-energy effects in κ − ( BEDT − TTF ) 2 Cu [ N ( CN ) 2 ] Br
Résumé
We report on the observation of phonon self-energy effects in the vicinity of Tc in the organic superconductor κ−(BEDT−TTF)2Cu[N(CN)2]Br, and their interpretation in the framework of strong electron-phonon coupling. The data qualify anomalous temperature dependence of the low-frequency phonons around and below Tc, and are consistent with an isotropic gap 2Δ0 close to 2.8 meV. Significant frequency shifts are recorded which allow us to evaluate the electron-phonon coupling λ for energetically weak phonons. The subsequent calculated values agree well with a superconducting transition at Tc∼11.6 K.