Abstract
We investigate phase transitions in a two-dimensional site-diluted superconducting array, using Monte Carlo simulations. The array is modeled via a site-diluted classical {ital XY} model on a square lattice in the regime {ital p}{sub {ital c}}{lt}{ital p}{lt}1, where {ital p} is the concentration of spins'' (representing the phases of the superconducting order parameters on the grains) and {ital p}{sub {ital c}} denotes the percolation threshold. In the unfrustrated case (zero magnetic field), we find that the Kosterlitz-Thouless (KT) transition temperature {ital T}{sub {ital c}}({ital p}) approaches zero according to the power law {ital T}{sub {ital c}}({ital p}){similar to}({ital p}{minus}{ital p}{sub {ital c}}){sup {kappa}} and {kappa}{approx}1.14, as {ital p}{r arrow}{ital p}{sub {ital c}} from above. To within the accuracy of the calculation, {kappa} equals the expected value of {ital t}, where {ital t}{approx}1.30 is the usual conductivity exponent. In the fully frustrated case, which in a perfect lattice ({ital p}=1) is characterized by a phase transition of combined KT- and Ising-like character, we find no Ising-like character in the diluted lattice. The apparent KT behavior is broadened over a considerable temperature range, compared to the case in the perfect lattice.
Published Version
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