Dynamical mean-field theory study of Nagaoka ferromagnetism

We revisit Nagaoka ferromagnetism in the U=infinity Hubbard model within the dynamical mean-field theory (DMFT) using the recently developed continuous time quantum Monte Carlo method as the impurity solver. The stability of Nagaoka ferromagnetism is studied as a function of the temperature, the doping level, and the next-nearest-neighbor lattice hopping t'. We found that the nature of the phase transition, as well as the stability of the ferromagnetic state, is very sensitive to the t' hopping. Negative t'=-0.1t stabilizes ferromagnetism up to higher doping levels. The paramagnetic state is reached through a first-order phase transition. Alternatively, a second-order phase transition is observed at t'=0. Very near half-filling, the coherence temperature T(coh) of the paramagnetic metal becomes very low and ferromagnetism evolves out of an incoherent metal rather than conventional Fermi liquid. We use the DMFT results to benchmark slave-boson method which might be useful in more complicated geometries.