Laboratoire de Physique Théorique
Toulouse - UMR 5152

Strongly interacting systems are known to often spontaneously develop exotic ground states under certain conditions. For instance, spin nematic phases have been discovered in various magnetic models. Such phases, which break spin symmetry but have no net local magnetization, have also been proposed by Nersesyan et al. [J. Phys. : Condens. Matter 3, 3353 (1991)] in the context of electronic models. We introduce a N-flavor microscopic model that interpolates from the large-N limit, where mean field is valid and such a nematic phase occurs, to the more realistic N=1 case. By using a sign-free quantum Monte Carlo, we show the existence of a spin nematic phase (analogous to a spin flux phase) for finite N ; when N decreases, quantum fluctuations increase and this phase ultimately disappears in favor of an s-wave superconducting state. We also show that this nematic phase extends up to a finite critical charge doping. Dynamical studies allow us to clarify the Fermi surface property : in the nematic phase at half-filling, it consists of four points and the low-energy structure has a Dirac conelike shape. Under doping, we observe clear signatures of Fermi pockets around these points. This is one of the few examples where numerical simulations show how quantum fluctuations can destroy a large-N phase.