Calculation of the singlet-triplet gap of the antiferromagnetic Heisenberg model on a ladder
Mohamed Moussadek Azzouz, Liang Chen, S. Moukouri
The ground-state energy and the singlet-triplet energy gap of the antiferromagnetic Heisenberg model on a ladder is investigated using a mean-field theory and the density-matrix renormalization group. Spin-wave theory shows that the corrections to the local magnetization are infinite. This indicates that no long-range order occurs in this system. A flux-phase state is used to calculate the energy gap as a function of the transverse coupling, ${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$, in the ladder. It is found that the gap is linear in ${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$ for ${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$\ensuremath{\gg}1 and goes to zero for ${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$\ensuremath{\rightarrow}0. The mean-field theory agrees well with the numerical results.
arXiv:cond-mat/9404067•Physical review. B, Condensed matter•Sep 1, 1994•63 citations