Difference between KT and ferro-para phase transitions in 2D

[wdlang]

i cannot see the reason

what makes KT phase transition different from the ferro-para phase transition of the 2D ising model?

 

[atyy]

There is no local order parameter in the KT transition, so it's "topological" rather than "symmetry breaking".

http://www.itp.uzh.ch/~llucas/projects/proseminar.pdf
http://www.phy.cuhk.edu.hk/course/2011-2012/1/phys5510/download/0/Ch11%20KT%20transition.pdf
http://www.mit.edu/~levitov/8.334/notes/XYnotes1.pdf