Phase transitions in 2D $J_1-J_2$ model with arbitrary signs of exchange interactions

A. V. Miheyenkov, A. V. Shvartsberg, A. F. Barabanov

The ground state of the $S=1/2$ $J_1-J_1$ Heisenberg model on the 2D square lattice with arbitrary signs of exchange constants is considered. States with different spin long-ra…