Superconductivity of repulsive carriers

We present the concept of Coulomb repulsion-induced superconducting pairing with large momentum and its application to a qualitative explanation of the underlying properties of cuprates. At low doping, the Fermi surface of the cuprates has the form of hole pockets with both mirror and conventional nesting promoting the superconducting and an insulating pairing, respectively. The kinematic constraint results in a cutoff of large momentum transfers under the Coulomb repulsion. The pairing potential turns out to be oscillating in the real space and ensures a rise of both bound and quasi-stationary states of two particles. The latter can be considered as developed fluctuations of the two-component superconducting order parameter apparent above the transition temperature. The relative phase of the components, as it follows from the Ginzburg-Landau phenomenology, can be associated with an orbital antiferromagnetic order. The competition between the superconducting and insulating orbital antiferromagnetic states leads to the natural explanation of the phase diagram of the cuprates. We explain an universal dependence of the superconducting transition temperature on the number of layers in the unit cell observed in homologous cuprate families. (C) 2007 Elsevier B.V. All rights reserved.