Bandwidth tuning triggers interplay of charge order and superconductivity in two-dimensional organic materials

We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor $beta^{primeprime}$-(BEDT-TTF)2 SF5 CH2 CF2 SO3 both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and investigating the in-plane dynamical response by infrared reflectance spectroscopy. The decrease of effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing on their interplay. We compare the results of our experiments with calculations on the extended Hubbard model.