Spontaneous symmetry breaking in Josephson junction arrays

The superconductor–insulator transition in the 2DXY model is identified as a spontaneous symmetry breaking. The strong size dependence in the spontaneous symmetry breaking predicts an order of magnitude increase   in the critical coupling constant EJ/TEJ/T with the array size. The order of magnitude change experimentally observed in the critical coupling constant EJ/ECEJ/EC from a single Josephson junction to the 48×4048×40 arrays may be accounted for likewise with an opposite tendency in the quantum phase transition; the critical EJ/ECEJ/ECdecreases with the array size.