Monte Carlo studies of the ordering of ceramic superconductors: Chiral-glass, orbital-glass, and nonlinear susceptibilities

Abstract

Static and dynamic properties of the intergranular ordering of ceramic superconductors are studied by Monte Carlo simulations on a three-dimensional lattice model of a Josephson-junction array with finite selfinductance. Both cases of d-wave and s-wave pairing symmetries are studied. In the case of d-wave ceramics, intrinsic frustration effects combined with quenched randomness lead to the glassy behavior reminiscent of the spin glass even in zero magnetic field. It is found that the zero-field nonlinear susceptibility exhibits a negatively divergent behavior, suggesting the occurrence of a cooperative transition into an ordered state characterized by the random freezing of chirality or flux. In this ''chiral-glass'' state, global Z 2 time-reversal symmetry appears to be broken spontaneously with keeping the U͑1͒ gauge symmetry. Dynamic simulations on the linear ac susceptibility suggest that d-wave ceramics exhibits much stronger dissipation than s-wave ceramics in the low-frequency regime. In the case of s-wave ceramics, standard superconducting transitions with broken U͑1͒ gauge symmetry occurs where nonlinear susceptibility exhibits only a very weak anomaly. Implications to experiments on high-T c ceramics are discussed.

Paramagnetic Meissner effect and related dynamical phenomena

“…The Monte Carlo simulations [145] showed that the PME is clearly visible for a very small inductanceL = 0.1. This result compatible with the conclusion in the previous section thatL c = 0 for the multi-loop model.…”

“…20, a paramagnetic behavior is shows up in FC regime in the field range h ≤ 1 (roughly corresponding to Φ ext ∼ Φ 0 /4), where the dimensionless field h is defined as [145] …”

“…This shortcoming may be amended in the multi-loop model [12,145] where the interaction between loops is taken into account.…”

“…For d-wave ceramics J ij is assumed to take the value -J (π-junction) with probability c and +J (0-junction) with probability (1-c) [12]. In the s-wave model J ij is always positive ("ferromagnetic" interaction) but distributed uniformly between 0 and 2π [145].…”

Dynamical reentrance and geometry imposed quantization effects in Nb–AlOx–Nb Josephson junction arrays

“…resulting from the presence of magnetic impurities in the junction (Bulaevskii et al 1977, Kusmartsev 1992 or from unconventional pairing symmetry (Kawamura and Li 1996).…”