Laboratoire de Physique Théorique
Toulouse - UMR 5152

We study the phase diagram of the Heisenberg model on the Honeycomb lattice with antiferromagnetic interactions up to third neighbors along the line $J_2=J_3$, where it describes the strong coupling limit of the Hubbard model at half-filling. Using the Schwinger boson technique followed by a mean field decoupling and exact diagonalization for finite systems we find an intermediate phase where quantum disorder is predicted in the strong quantum limit $(S=\frac12)$. Both techniques provide consistent results which allow us to predict the existence of an intermediate phase with a spin gap and short range N\’eel correlations. The relation of these results with recent experiments is discussed.