Raman-active intramolecular CH2 and C=C vibrations and microwave surface impedance studies of the organic superconductor κ-[bis(ethylenedithio)tetrathiafulvalene]2Cu(N(CN)2)Br

Abstract

We report a systematic Raman study of intramolecular vibrations for single crystals of the organic superconductor κ-(BEDT-TTF)2Cu(N(CN)2)Br in both the normal and superconducting states. The study has focused on the C=C stretching vibrations and the CH2 scissoring modes. From the frequency of the C=C-ring-stretching Raman mode ν3(Ag) we estimate the average charge transfer ρ=0.4 on the BEDT-TTF donor at 295 K while a metal-insulator transition region around 190 K is confirmed by a frequency discontinuity of the C=C ring vibrations. Frequency of CH2 vibrational modes show a discontinuity at Tc that indicates a selective change in the interaction between the ethylene groups of the donor molecule BEDT-TTF and the anion (CU(N(CN)2)Br)− while the frequency of the C=C-ring-stretching mode is blue shifted just above Tc, suggesting a possible renormalization of the electron-molecular interaction. Also, in order to complement our Raman experiments and to appreciate both the crystal quality and the nature of the superconducting state in our studied samples, we present measurements, as a function of temperature, of the microwave surface impedance.

Source-reported materials — not catalogue approval

Similar papers