Ground state and finite temperature signatures of quantum phase transitions in the half-filled Hubbard model on a honeycomb lattice

Details Ground state and finite temperature signatures of quantum phase transitions in the half-filled Hubbard model on a honeycomb lattice Ground state and finite temperature signatures of quantum phase transitions in the half-filled Hubbard model on a honeycomb lattice

2004-06-22

arxiv.org/abs/cond-mat/0406535v1

Phys. Rev. B 72, 085123 (2005)

Physics

Condensed Matter

Strongly Correlated Electrons

11 pages, 19 figures

Scientific paper

10.1103/PhysRevB.72.085123

We investigate ground state and finite temperature properties of the half-filled Hubbard model on a honeycomb lattice using quantum monte carlo and series expansion techniques. Unlike the square lattice, for which magnetic order exists at T=0 for any non-zero $U$, the honeycomb lattice is known to have a semi-metal phase at small $U$ and an antiferromagnetic one at large $U$. We investigate the phase transition at T=0 by studying the magnetic structure$and compressibility using quantum monte carlo simulations and by calculating the sublattice magnetization, uniform susceptibility, spin-wave and single hole %single-particle dispersion using series expansions around the ordered phase. Our results are consistent with a single continuous transition at $U_c/t$ in the range 4-5. Finite temperature signatures of this phase transition are seen in the behavior of the specific heat, $C(T)$, which changes from a two-peaked structure for $U>U_c$ to a one-peaked structure for $U < U_c$. Furthermore, the $U$ dependence of the low temperature coefficient of $C(T)$ exhibits an anomaly at $U \approx U_c$.

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