Superconductivity Induced by Negative Centers

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We study the effect of random dilution of attraction centers on electron pairing in a generalization of the negative U Hubbard model where the interaction Uᵢ, defined on the two dimensional lattice, can be -|U| and 0 with probability c and 1-c depending on the lattice site i. Using the determinant quantum Monte Carlo approach, we find the critical concentration c₀ of negative centers which leads to superconductivity, and show how the evolution of the local density on the two types of sites lends insight into the formation of global phase coherence.