Quantum critical transition from charge-ordered to superconducting state   in the triangular lattice negative-U extended Hubbard model
  We demonstrate a robust frustration-driven charge-order to superconductivity transition in the half-filled negative-U extended Hubbard model. Superconductivity extends over a broad region of the parameter space. We argue that the model provides the correct insight to understanding unconventional superconductivity in the organic charge-transfer solids and other quarter-filled systems. 
S. Mazumdar and R.T. Clay