Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2001-03-08
Physics
Condensed Matter
Strongly Correlated Electrons
To be published in J. Phys. Soc. Jpn. 70-6. 4 pages with 3 eps figures
Scientific paper
10.1143/JPSJ.70.1483
As a model for the B 2pz 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 $U_c/t \simeq 3.6$, 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 2pz bands is destroyed by carrier doping.
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