Electron-phonon coupling in κ-(bedt-ttf)2cu(ncs)2 organic superconductor studied by raman scattering spectroscopy

Low frequency Raman data for κ-(ET)2Cu(NCS)2 (Tc = 10.4 K) are reported. Measurements have been performed in a wide range of temperatures (1.5–100 K) and frequency hardening related to the superconducting transition has been observed for all the low-lying coupled phonons. The measured relative frequency shifts are lower than those previously reported for κ-(ET)2Cu[N(CN)2]Br (Tc=11.6 K), but the behavior of the two systems is similar and indicates a significant strength of the intermolecular electron-phonon coupling. The effects of isotopic substitutions (13C434S8 and 2H8) in ET molecules on the low frequency Raman active phonons of κ-(ET)2Cu(NCS)2 are also reported. They give the first direct experimental confirmation to the suggested lattice softening induced by deuteration.