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Destruction of Superconductivity by Impurities in the Attractive Hubbard Model
We study the effect of U=0 impurities on the superconducting and
thermodynamic properties of the attractive Hubbard model on a square lattice.
Removal of the interaction on a critical fraction of of the sites results in the destruction of off-diagonal long range order
in the ground state. This critical fraction is roughly independent of filling
in the range , although our data suggest that might be somewhat larger below half-filling than at . We also
find that the two peak structure in the specific heat is present at both
below and above the value which destroys long range pairing order. It is
expected that the high peak associated with local pair formation should be
robust, but apparently local pairing fluctuations are sufficient to generate a
low temperature peak