Electronic Band Properties And Superconductivity In La2-Yxycuo4

The results of electronic-structure calculations for tetragonal ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ provide insight concerning the origin of high-temperature superconductivity in the ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{y}}$${\mathrm{X}}_{\mathrm{y}}$${\mathrm{CuO}}_{4}$ alloys. A half-filled Cu(3d)-O(2p) band with two-dimensional character and a nearly square Fermi surface produces a Peierls instability for y=0 that opens a semiconductor gap over the Fermi surface. Alloying with divalent or tetravalent atoms should spoil the nesting features while maintaining the strong coupling of O phonons to the conduction electrons.