A Raman study of the organic superconductor κ-(BEDT-TTF)₂Cu(SCN)₂ at high pressure

The Raman spectrum of the organic superconductor κ-(BEDT-TTF)₂Cu(SCN)₂ has been measured under hydrostatic pressures up to 1.5 GPa at room temperature. Linear variation of all the observed modes with pressure confirms the absence of a structural phase transition in this pressure range. The Raman spectra reveal three low-frequency features that rapidly stiffen with pressure, dln ν/d P = 5-17% GPa^-1; comparison with x-ray data indicates assignment to lattice modes. By contrast, most Raman-active intramolecular vibrations stiffen by only 0.1-1% GPa^-1. Contrary to expectations from a previous high-pressure x-ray study, we do not observe a pressure induced splitting of the 3A_g mode.