3
votes
0answers
59 views

Neel order and O(3) model

The coarse grained fluctuations of the Neel order parameter in the half integer spin anti-ferromagnetic Heisenberg model is described by the O(3) non-linear sigma model with a strange berry phase ...
1
vote
1answer
127 views

Is water a gas at critical density, room temperature?

I am quoting Chaikin, Lubensky, Principles of Condensed Matter Physics, p. 4. Now suppose we have a closed container of water vapor at a density of 0.322 g/cc at room temperature. As the ...
3
votes
2answers
231 views

Why is a critical system equal to a gapless system?

In condensed matter physics, people often say that a system without energy gap is a critical system. What does it mean? Any help is appreciated!