High-temperature superconductivity and band antiferromagnetism

We analyze the competition between high-temperature superconductivity (SC) and antiferromagnetism (AF) using the extended Hubbard model containing following matrix elements in the Hamiltonian: Hund's on-site field F-H, single-site Coulomb repulsion U = (i, i vertical bar 1/r vertical bar i, i), two-site charge-charge, exchange, pair exchange and assisted hopping interactions V = (i, j vertical bar 1/r vertical bar i, j), J = (i, j vertical bar 1/r vertical bar j, i), J' = (i, i vertical bar 1/r vertical bar j, j), Delta t = (i, i vertical bar 1/r vertical bar j, i). In our model, we introduce the possibility of AF ordering by dividing the crystal lattice into two interpenetrating sub-lattices alpha,beta. We use Hartree-Fock (H-F) approximation for all interactions except the strong on-site Coulomb repulsion. The self-energies Sigma(sigma)(gamma)(epsilon) (gamma = alpha, beta) are calculated within the coherent potential approximation (CPA). To obtain the SC transition temperature T-C and the Neel's temperature T-N we solve the coupled equations of motion for the Green's functions. We present numerical results. They show that the AF at half-filling destroys the superconductivity of the so-wave symmetry. Increase of the Coulomb repulsion in the CPA causes increasing dumping of so-wave SC, shifts it away from the half-filling point, enhances SC temperature for sub-lattice magnetic moments; 0 < m < 0.28 mu(B). (c) 2005 Elsevier B.V. All rights reserved.