Electronic structure of planar superconducting systems.: From finite to extended model

摘要: Abstract A 4-site 4-electron model is extended to a square planar CuO 2 sheet. The degeneracy at the Fermi level can be split in different ways and this results charge density wave ground state, with alternating charges on metal sites, or an anti-ferromagnetic state spin correlation. If these two states are nearly equal energy, magnetic may appear perpendicular field, persistent currents paired spins. tight-binding used for systems L loops (2 ) sites. -fold degenerate eigenvalue x =0, consistent Van Hove singularity, has exact eigenvector solutions which as generators other possible solutions. In exist of hole-doped infinite system. novel explanation given `extended saddle point singularity' energy bands below T c . Some properties type II superconductors also explained, such d-wave symmetry pair function.