Plasmons and high-temperature superconductivity in alloys of copper oxides

The two-dimensional character of the electronic structure of M-N-Cu-O alloys, with M=La,Y and N=Ba,Sm,..., is shown to favor the formation of ``acoustic'' plasmons at energies above the acoustic phonons. Providing that the Fermi energy intersects a small pocket of electrons (or holes) in addition to the expected occupation of a primary electron (or hole) band, the plasma oscillations of the secondary charge carriers may provide a mechanism for room-temperature superconductivty.