Antiferromagnetism of the Hubbard Model on a Layered Honeycomb Lattice : Is MgB_2 a Nearly-Antiferromagnetic Metal? : Condensed Matter: Electronic Properties, etc.

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As a model for the B 2p_z bands of MgB_2, 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 U_c/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 U_c = 0. From these facts, we discuss that MgB_2 is possibly a nearly-AF metal, where the AF of the 2p_z bands is destroyed by carrier doping.
社団法人日本物理学会の論文
2001-06-15