arXiv:1504.01334 · Europhysics Letters (EPL)
Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J 1 -J 2 Heisenberg model
Tarik P. Cysne, M. B. Silva Neto
Abstract
We obtain the complete magnetic phase diagram of the two-dimensional antiferromagnetic Heisenberg model, , within the framework of the O ( N ) nonlinear sigma model. We find two magnetically ordered phases, one with Néel order, for , and another with collinear order, for , separated by a nonmagnetic region, for , where a gapped spin liquid is found. The transition at is of the second order while the one at is of the first order and the spin gaps cross at . Our results are exact at N → ∞ and agree with numerical results from different methods.