Phase and vortex correlations in Josephson-junction arrays at irrational frustration

Phase coherence and vortex order in a Josephson-junction array at irrational frustration are studied by extensive Monte Carlo simulations using the parallel tempering method. A scaling analysis of the correlation length of phase variables in the full equilibrated system shows that the critical temperature vanishes with a power-law divergent correlation length and critical exponent $\nu_{ph}$, in agreement with recent results from resistivity scaling analysis. A similar scaling analysis for vortex variables reveals a different critical exponent $\nu_{v}$, suggesting that there are two distinct correlation lengths associated with a decoupled zero-temperature phase transition.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Zero-temperature transition and correlation-length exponent of the frustrated XY model on a honeycomb lattice

Phase coherence and vortex order in the fully frustrated XY model on a two-dimensional honeycomb lattice are studied by extensive Monte Carlo simulations using the parallel tempering method and finite-size scaling. No evidence is found for an equilibrium order-disorder or a spin/vortex-glass transition, suggested in previous simulation works. Instead, the scaling analysis of correlations of phase and vortex variables in the full equilibrated system is consistent with a phase transition where the critical temperature vanishes and the correlation lengths diverge as a power-law with decreasing temperatures and corresponding critical exponents $\nu_{ph}$ and $\nu_{v}$. This behavior and the near agreement of the critical exponents suggest a zero-temperature transition scenario where phase and vortex variables remain coupled on large length scales.Comment: 8 pages, 10 figure

Phase-coherence transition in granular superconductors with π\pi junctions

We study the three-dimensional XY-spin glass as a model for the resistive behavior of granular superconductors containing a random distribution of $\pi$ junctions, as in high-$T_c$ superconducting materials with d-wave symmetry. The $\pi$ junctions leads to quenched in circulating currents (chiralities) and to a chiral-glass state at low temperatures, even in the absence of an external magnetic field. Dynamical simulations in the phase representation are used to determine the nonlinear current-voltage characteristics as a function of temperature. Based on dynamic scaling analysis, we find a phase-coherence transition at finite temperature below which the linear resistivity should vanish and determine the corresponding critical exponents. The results suggest that the phase and chiralities may order simultaneously for decreasing temperatures into a superconducting chiral-glass state.Comment: 5 pages, 1 figure, Proc. of ICM 2000, to appear in J. Magn. Magn. Mate

Zero-temperature resistive transition in Josephson-junction arrays at irrational frustration

We use a driven Monte Carlo dynamics in the phase representation to determine the linear resistivity and current-voltage scaling of a two-dimensional Josephson-junction array at an irrational flux quantum per plaquette. The results are consistent with a phase-coherence transition scenario where the critical temperature vanishes. The linear resistivity is nonzero at any finite temperatures but nonlinear behavior sets in at a temperature-dependent crossover current determined by the thermal critical exponent. From a dynamic scaling analysis we determine this critical exponent and the thermally activated behavior of the linear resistivity. The results are in agreement with earlier calculations using the resistively shunted-junction model for the dynamics of the array. The linear resistivity behavior is consistent with some experimental results on arrays of superconducting grains but not on wire networks, which we argue have been obtained in a current regime above the crossover current.Comment: 7 pages, 5 figures, to appear in Phys. Rev.