Spin Liquid Phase in the Hubbard Model on the Honeycomb Lattice

Using projective (${T=0}$) quantum Monte Carlo simulations, we investigate the ground-state properties of the half-filled Hubbard model on the honeycomb lattice. We provide evidence for a gapped phase separating the weak-coupling semi-metal and the antiferromagnetically ordered phase at strong coupling. Exploring quasi-particle and spin excitation gaps, flux quantization as well as probing for various correlation functions, we conclude that in this intermediate interaction region the system exhibits no long-range magnetic or bond-order nor superconductivity. Several proposals on novel phases in related models have been put forward, whereas our simulations establish a spin liquid - even in the absence of magnetic frustration.