Two-dimensional Josephson junction array at an irrational frustration

The IV characteristics of a two-dimensional square Josephson junction array are studied at various frustrations (f = 1/3, 2/5, 8/21, and 0.6180) with particular attention to those at f = 0.6180, an approximation of the irrati onal filling f = Omega [Omega = (root5 - 1)/2]. The IV characteristics at f = 0.6180 exhibit a scaling behavior with nearly the same critical exponent s, scaling function, and critical temperature as for f = 2/5 and 8/21. The similarity in the characteristics of the phase transitions suggests that th e low-temperature phase at the irrational filling is not a vortex glass as expected by some, but possibly a quasi-ordered state with a low-order ratio nal structure as the principal structure.