The pressure dependence of many-body interactions in the organic superconductorκ-(BEDT-TTF)2Cu(SCN)2(BEDT-TTF ≡ bis(ethylene-dithio)tetrathiafulvalene): a comparison of high-pressure infraredreflectivity and Raman scattering experiments

Abstract

We determine the pressure dependence of the electron–phonon coupling inκ-(BEDT-TTF)2Cu(SCN)2by comparison of high-pressure Raman scattering and high-pressure infrared (IR)reflectivity measurements. The Raman active molecular vibrations ofthe BEDT-TTF dimers stiffen by 0.1–1% GPa−1.In contrast, the corresponding modes in the IR spectrum are observed at lowerfrequency, with a pressure dependence of 0.5–5.5% GPa−1,due to the influence of the electron–phonon interaction. Both dimercharge-oscillation and phase-phonon models are employed to extract thepressure dependence of the electron–molecular vibration coupling for thesemodes. Analysis of our data suggests that the reduction of electron–phononcoupling under pressure does not account for the previously observedsuppression of superconductivity under pressure and that electron–electroninteractions may contribute significantly to the pairing mechanism.