Mean field theory of superconductivity in frustrated 2D-XY magnets

Abstract

We consider the two-dimensional antiferromagnetic classical XY model on a square lattice with frustrated plaquettes introduced by dilute doping of ferromagnetic bonds. These ferromagnetic bonds carry positive electronic charges of the holes. A pairing potential is derived and the energy spectrum of a hole pair is discussed for the possibility of bound states. In the long distance approximation, the dipolar interaction between canted local states is derived and discussed in the mean field in both reciprocal space and real space. BCS type calculation of the pairing potential is formulated for the lowest angular momentum gap function. The odd parity gap yields higher transition temperature then the corresponding even parity one. Application to La 2CuO 4 yields critical temperature in the order of 40 K. Implications of this effective attraction mediated by the frustrated plaquettes in the XY model are suggested for other types of two-dimensional magnets. Possible extensions of the model to incorporate Ising anisotropy and interplanar coupling are discussed.