arXiv:1209.6091 · Physical Review B
Plaquette resonating valence bond state in a frustrated honeycomb antiferromagnet
R. Ganesh, Satoshi Nishimoto, Jeroen van den Brink
Abstract
We study the proposed plaquette resonating valence bond (pRVB) state in the honeycomb lattice ${J}_{1}\ensuremath{-}{J}_{2}$ model with frustration arising from next-nearest-neighbor interactions. Starting with the limit of decoupled hexagons, we develop a plaquette operator approach to describe the pRVB state and its low-energy excitations. Our calculation clarifies that the putative pRVB state necessarily has $f$-wave symmetry: the plaquette wave function is an antisymmetric combination of the Kekul\'e structures. We estimate the plaquette ordering amplitude, ground-state energy, and spin gap as a function of ${J}_{2}/{J}_{1}$. The pRVB state is most stable around ${J}_{2}/{J}_{1}\ensuremath{\sim}0.25$. We identify the wave vectors of the lowest triplet excitations, which can be verified using exact diagonalization or density-matrix renormalization group (DMRG) studies. When ${J}_{2}$ is reduced, we can have either a deconfined quantum phase transition (QPT) or a first-order transition into a N\'eel state. When ${J}_{2}$ is increased, we surmise that the system will undergo a first-order phase transition into a state which breaks lattice rotational symmetry.