Antiferromagnetism of the Hubbard Model on a Layered Honeycomb Lattice - Is MgB₂ a Nearly-Antiferromagnetic Metal? -

الأصل · EN

As a model for the B 2pz bands of MgB₂, a half-filled Hubbard model on a honeycomb lattice is studied, and a possibility of an antiferromagnetism (AF) at the ground state is examined by Monte Carlo calculations as well as a random phase approximation method. On a single-layer honeycomb lattice, a paramagnetic to AF phase transition occurs at a finite value of the repulsion energy Uc/t ≃ 3.6, due to the loss of the density of states at the fermi level. On a layered honeycomb lattice, however, inter-layer hopping term creates a perfect nesting of the fermi surface, and leads the AF with Uc=0. From these facts, we discuss that MgB₂ is possibly a nearly-AF metal, where the AF of the 2pz bands is destroyed by carrier doping.