A DMRG study of the half-filled Hubbard model on a Bethe lattice: a signature of the Mott-Hubbard transition
Marie-Bernadette Lepetit, Maixent Cousy
Abstract
The half-filled Hubbard model on the Bethe lattice with coordination number $z=3$ is studied using the density-matrix renormalization group (DMRG) method. Ground-state properties such as the energy $E$, average local magnetization $ $, its fluctuations $ - ^2$ and various spin correlation functions $ - $ are determined as a function of the Coulomb interaction strength $U/t$. The calculated local magnetic moments $ $ increase monotonically with increasing Coulomb repulsion $U/t$ forming an antiferromagnetic spin-density-wave state which matches the two sublattices of the bipartite Bethe lattice. At large $U/t$, $ $ is strongly reduced with respect to the saturation value 1/2 due to exchange fluctuations between nearest neighbors (NN) spins ($| |\simeq 0.35$ for $U/t\to +\infty$). $ - ^2$ shows a maximum for $U/t=2.4$--2.9 which results from the interplay between the usual increase of $ $ with increasing $U/t$ and the formation of important permanent moments $ $ at large $U/t$. NN sites show antiferromagnetic spin correlations which increase with increasing Coulomb repulsion. In contrast next NN sites are very weakly correlated over the whole range of $U/t$. The accuracy of the DMRG results is discussed by comparison with tight-binding exact results, independent DMRG calculations for the Heisenberg model and simple first-order perturbation estimates.