From valence bond solid to unconventional superconductivity in the organic charge-transfer solids

We show that superconductivity is absent within the frac(1, 2)-filled band triangular lattice repulsive Hubbard model that has been proposed for organic charge-transfer solids. We posit that organic superconductivity is rather reached from a bond-charge density wave that either constitutes the insulating state proximate to superconductivity, or is extremely close in energy to the antiferromagnetic state, and replaces the latter under pressure. The bond-charge density wave can be described within an effective attractive U extended Hubbard Hamiltonian with repulsive nearest neighbor interaction V. A first-order transition from the insulating to the superconducting state occurs within the model with increasing frustration.