Superconductivity coupled to density waves

We investigate a mechanism of superconductivity on the basis of the nested-Fermi-liquid theory. A set of parquet equations is derived to investigate the instability towards superconductivity and spin- or charge-density-wave states. The phase diagram is examined on the basis of the parquet equations. We find that the polarization mode of the marginal-Fermi-liquid-type is of vital importance to superconductivity. We also discuss the properties of a superconductor on the basis of the nested Fermi liquid.