Dynamical screening and electron-mediated superconductivity in intercalated layered metallochloronitrides

Metallochloronitrides are layered conductors that have recently been found to superconduct at critical temperatures up to T-c similar or equal to 26 K. It is known that the electron-phonon interaction is small in these systems, so that the conventional pairing mechanism through exchange of phonons is unable to provide for such high T(c)s. We show that the dominant contribution to the pairing interaction in these materials comes from the exchange of low-energy collective modes, specific to layered conductors. The existence of such acoustic plasmons results from the incomplete screening of the Coulomb interaction perpendicular to the conducting planes which expresses itself in the dynamical nature of the screened Coulomb interaction.