Point Defect Disorder in Models of High Temperature Superconductivity

Abstract

Experimental high T _c systems are intrinsically strongly disordered by point defects. Here we consider two possible consequences of this fact: 1) The magnetic phases of prominent models for high T _c are strongly affected. We present numerical calculations of the phase diagram of the Hubbard model as a function of the concentration of point defects and of the band filling in the Hartree Fock approximation. The results may explain the failure to experimentally observe a spin density wave phase predicted by Hartree Fock calculations without defects. 2) The superconductivity of the system may be strongly affected. We consider a model in which the pairing interactions are generated by point defects. We present numerical data on the density of states, T _c and local charge density in the BCS approximation, while taking full account of the disorder. The stability of the BCS state was also checked using a variational Monte Carlo calculation.