Phonon Self-Energy Effects In Kappa-(Bedt-Ttf)(2)Cu[N(Cn)(2)]Br

We report on the observation of phonon self-energy effects in the vicinity of T-c in the organic superconductor kappa-(BEDT-TTF)(2)Cu[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 T-c, and are consistent with an isotropic gap 2 Delta(0) close to 2.8 meV. Significant frequency shifts are recorded which allow us to evaluate the electron-phonon coupling lambda for energetically weak phonons. The subsequent calculated values agree well with a superconducting transition at T(c)similar to 11.6 K.