Raman and FTIR studies of phase transitions in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl

The Raman active CC stretching modes and CH2 deformation modes and the infrared active CN mode are studied as a function of temperature in κ-(BEDT-TTF)2Cu(N(CN)2)Cl under pressure. Effects of the structural and superconducting transitions on these excitations are analyzed. The CH2 and CN modes are sensitive to the thermal expansion around 80 K and to a possible superlattice transition around 160 K while the CC stretching Raman modes ν2(Ag) are influenced by the formation of the superconducting state.