Mechanism of superconductivity in organic metals

The “fundamental” mechanism of superconductivity in organic metals has been a mystery for a long time. Various mechanisms, such as interactions mediated by excitons, internal phonons, or paramagnons have been proposed. We performed a calculation for the phononmediated BCS model, under conditions of very strong coupling, with external phonons (such as librons). We find that the large ionic dielectric constant (ɛ0≈20) has a profound effect, increasing Tc by about an order of magnitude, by its effect on the electron-phonon matrix element. We find for a 2D metal a maximum Tc of approximately (Tc)max≈0.1(e2/2ac)√2m/M where 2ac is the length of the “metallic” portion of the molecule, m the electronic band mass, and M the ionic mass. Detailed behavior of the sc tunneling, and resistivity in the normal state, are in full accord with this theory.