A dynamical mean-field theory study of Nagaoka ferromagnetism

We revisit Nagaoka ferromagnetism in the two-dimensional U = ∞ Hubbard model using the dynamical mean-field theory (DMFT). A recently developed continuous time quantum Monte Carlo method is applied to solve the DMFT impurity problem. The stability of Nagaoka ferromagnetism is studied as a function of both the nearest-neighbor lattice hopping t and the next-nearest-neighbor lattice hopping t. It is shown that the ferromagnetic state is strongly stabilized when t is negative. A second order ferromagnetic to paramagnetic transition at t = 0 changes to a first order transition at t/t = −0.1. At a finite temperature T close to half filling, ferromagnetism becomes unstable as T exceeds the coherence temperature Tcoh, while in the large doping regime the ferromagnetism emerges from a more conventional fermi liquid . We use the DMFT results to benchmark slave-boson calculations which can be used to study more complicated geometries.