Ordering of a frustrated Josephson-coupled network system of sub-micron-scale grains

Ordering characteristics of a superconductive ceramic of YBa2Cu4O8 are newly examined experimentally by analyzing the nonlinear magnetic responses, in order to discuss intergrain ordering of frustrated Josephson-coupled network system of sub-micron-scale grains below the superconductive critical temperature. The derived nonlinear magnetic susceptibility χ2 shows a symmetric negative divergence at the temperature corresponding to the intergrain ordering point Tc2. The result indicates that the ordering of a 3D XY-type spin glass is associated with the same singularity of nonlinear chiral susceptibility at the temperature.