Magnetic quantum phase transitions of the two-dimensional antiferromagnetic J1-J2 Heisenberg model
Instituto de Física, Universidade Federal do Rio de Janeiro - Caixa Postal 68528, Brasil
Received: 23 July 2015
Accepted: 13 November 2015
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.
PACS: 78.30.-j – Infrared and Raman spectra / 63.20.Ry – Anharmonic lattice modes
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