2008/07/24 by Felipe Mondaini, Thereza Paiva, Raimundo R. dos Santos +2
Physics and Astronomy · #Advanced Condensed Matter Physics #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.78.174519
9 two-column pages, 14 figures, RevTeX
arxiv created 2008/07/24 · openalex publication_date 2008/11/19 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We have considered the half-filled disordered attractive Hubbard model on a square lattice, in which the on-site attraction is switched off on a fraction f of sites, while keeping a finite U on the remaining ones. Through quantum Monte Carlo simulations for several values of f and U and for system sizes ranging from 8\ifmmode×\else\texttimes\fi8 to 16\ifmmode×\else\texttimes\fi16, we have calculated the configurational averages of the equal-time pair structure factor Ps and, for a more restricted set of variables, the helicity modulus \ensuremathρs, as functions of temperature. Two finite-size scaling Ans"atze for Ps have been used: one for zero temperature and the other for finite temperatures. We have found that the system sustains superconductivity in the ground state up to a critical impurity concentration fc, which increases with U, at least up to U=4 (in units of the hopping energy). Also, the normalized zero-temperature gap as a function of f shows a maximum near f\ensuremath∼0.07 for 2\ensuremath\lesssimU\ensuremath\lesssim6. Analyses of the helicity modulus and of the pair structure factor led to the determination of the critical temperature as a function of f for U=3, 4, and 6: they also show maxima near f\ensuremath∼0.07, with the highest Tc increasing with U in this range. We argue that, overall, the observed behavior results from both the breakdown of charge-density-wave-superconductivity degeneracy and the fact that free sites tend to ``push'' electrons toward attractive sites; the latter effect being more drastic at weak couplings.