Ferromagnetic phase transitions in the single-band Hubbard model

Abstract

The authors investigate the zero-temperature phase diagram of the single-band Hubbard model in two and three dimensions, with an emphasis on the region where ferromagnetism occurs. To determine the equilibrium value of the magnetization m, the authors compute the expectation value of the Hamiltonian using a Gutzwiller variational wavefunction for arbitrary values of m. Analytic calculations are performed using an improved Gutzwiller-type approximation. In two dimensions the authors predict a first-order transition from a saturated ferromagnetic state to a paramagnetic state. In three dimensions they find both a first-order and a second-order transition depending on the values of the Coulomb repulsion U and the hole concentration delta . They also discuss the possibility that the system phase separates into a region with a large hole concentration and a region with few holes.