Breaking-symmetry fields in two-dimensional planar models

Abstract

The planar model in presence of symmetry-breaking fields is studied on square and triangular lattices by Monte Carlo simulation. In the square model a phase transition with non-universal critical exponents is found. In the triangular lattice a Berezinskii–Kosterlitz–Thouless phase is observed over a finite temperature region between the low-temperature ordered phase and the high-temperature paramagnetic phase.