• DOI:10.1103/PhysRevB.97.014413
• Corpus ID: 103258307

Spontaneous dimerization and moment formation in the Hida model of the spin-1 kagome antiferromagnet

@article{Ghosh2017SpontaneousDA,
  title={Spontaneous dimerization and moment formation in the Hida model of the spin-1 kagome antiferromagnet},
  author={Pratyay Ghosh and Brijesh Kumar},
  journal={Physical Review B},
  year={2017},
  volume={97},
  pages={014413}
}

• P. Ghosh, B. Kumar
• Published 22 September 2017
• Materials Science
• Physical Review B

The Hida model, defined on a honeycomb lattice, is a spin-1/2 Heisenberg model of aniferromagnetic hexagons (with nearest-neighbor interaction, ${J}_{A}g0)$ coupled via ferromagnetic bonds (with exchange interaction, ${J}_{F}l0)$. It applies to the spin-gapped organic materials, $\mathrm{m}\text{\ensuremath{-}}\mathrm{MPYNN}\ifmmode\cdot\else\textperiodcentered\fi{}X$ (for $X=\mathrm{I},{\mathrm{BF}}_{4},{\mathrm{ClO}}_{4})$, and for $|{J}_{F}|\ensuremath{\gg}{J}_{A}$, it reduces to the spin-1 kagome Heisenberg antiferromagnet (KHA). Motivated by the recent finding of the trimerized singlet (TS) ground state for spin-1 KHA, we investigate the evolution of the ground state of the Hida model from weak to strong ${J}_{F}/{J}_{A}$ using mean-field triplon analysis and Schwinger boson mean-field theory. Our triplon analysis of the Hida model shows that its uniform hexagonal singlet (HS) ground state (for weak ${J}_{F}/{J}_{A})$ gives way to the dimerized hexagonal singlet (D-HS) ground state for $|{J}_{F}|/{J}_{A}\ensuremath{\gtrsim}1.26$ (which for strong ${J}_{F}/{J}_{A}$ approaches the TS state). From the Schwinger boson calculations, we find that the evolution from the uniform HS phase for spin-1/2 Hida model to the TS phase for spin-1 KHA happens through two quantum phase transitions: (1) the spontaneous dimerization transition at ${J}_{F}/{J}_{A}\ensuremath{\sim}\ensuremath{-}0.28$ from the uniform HS to D-HS phase and (2) the moment formation transition at ${J}_{F}/{J}_{A}\ensuremath{\sim}\ensuremath{-}1.46$, across which the pair of spin-1/2's on every FM bond begins to appear as a bound moment that tends to spin-1 for large negative ${J}_{F}$'s. The TS ground state of spin-1 KHA is thus adiabatically connected to the D-HS ground state of the Hida model. Our calculations imply that the $\mathrm{m}\text{\ensuremath{-}}\mathrm{MPYNN}\ifmmode\cdot\else\textperiodcentered\fi{}X$ salts realize the D-HS phase at low temperatures, which can be ascertained through neutron diffraction.