Electronic band properties and superconductivity in $\mathrmLa_2\mathrm-\mathrmy$$\mathrmX_\mathrmy$$\mathrmCuO_4$

The results of electronic-structure calculations for tetragonal La2CuO4 provide insight concerning the origin of high-temperature superconductivity in the La2-yXyCuO4 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.