arXiv:cond-mat/9807247 · Physical Review Letters
Quantum Phase Transitions in the Triangular-Lattice Bilayer Heisenberg Model
Rajiv R. P. Singh, N. Elstner
Abstract
We study the triangular-lattice bilayer Heisenberg model with antiferromagnetic interplane coupling ${J}_{\ensuremath{\perp}}$ and nearest-neighbor intraplane coupling $J\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\lambda}{J}_{\ensuremath{\perp}}$ by expansions in $\ensuremath{\lambda}$. For negative $\ensuremath{\lambda}$ a phase transition is found to an ordered phase at a ${\ensuremath{\lambda}}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.2636\ifmmode\pm\else\textpm\fi{}0.0001$, which is in the 3D classical Heisenberg universality class. For $\ensuremath{\lambda}>0$, we find a transition at a rather large ${\ensuremath{\lambda}}_{c}\ensuremath{\approx}1.2$. The universality class of the transition is consistent with that of Kawamura's 3D antiferromagnetic stacked triangular lattice. The spectral weight for the triplet excitations, at the ordering wave vector, remains finite at the transition, suggesting that a phase with free spinons does not exist in this model.