Experimental determination ofBEDT−TTF+electron-molecular vibration constants through optical microreflectance

Abstract

In the salt formed by bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with the $[{\mathrm{Mo}}_6{\mathrm{O}}_{19}{]}^{2\mathrm{-}}$ anion, the ${\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F}}^{+}$ cations form quasi-isolated dimers. For this reason $({\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F})}_2{\mathrm{Mo}}_6{\mathrm{O}}_{19}$ has been selected to experimentally evaluate the ${\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F}}^{+}$ microscopic parameters. Using the microreflectance technique we were able to collect polarized infrared/visible spectra from a single-crystal face. The analysis of the spectra in terms of the isolated dimer model yields reliable estimates of ${\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F}}^{+}$ electron-molecular vibration $\mathrm{}(e-mv)\mathrm{}$ coupling constants. The effective on-site electron-electron repulsion is also evaluated. A comparison is made with available theoretical estimates of $e-mv$ coupling constants. The possible role of $e-mv$ coupling in BEDT-TTF based superconductors is briefly discussed.