“…The conventional picture is that the XY -model phase transition is driven by a vortex binding mechanism [3,4]. This is in contrast to the customary picture of the step model [31,32,33,34,35,36,38]. Here, while the configuration space is the same as that of the XY -model, vortex formation is not believed to be energetically favourable given the discontinuous nature of the interaction function.…”