Charge-sensitive vibrational modes in BEDT-TTF salts: Signatures of charge ordering and site charge
The study investigates C=C stretching modes ($ u_{27}(b_{1u})$ and $ u_2(a_g)$) in BEDT-TTF salts to probe charge ordering. Linear relations show frequency shifts proportional to charge imbalance ($ ho$). While these relations confirm charge disproportionation, the observed frequency spread of over 20 cm$^{-1}$ creates a large uncertainty ($\Delta\rho \approx (\pm 0.045)e$) when trying to determine absolute site charges.