KIAS workshop "From correlated electrons to nanoscale materials"

at Korea Institute for Advanced Study (KIAS), Seoul, Korea

• Kwon Park
  
  Korea Institute for Advanced Study (KIAS)
  
  

  Title

  Valence Bond Solid on the Kagome Lattice

  Abstract

  One of the most promising candidate ground states for the quantum antiferromagnetic Heisenberg model on the Kagome lattice is the valence bond solid (VBS) with a 36-site unit cell. In this talk I present a theory of triplet excitation spectra about the VBS ground state using bond operator formalism, where dispersions of all 18 triplet modes in the reduced Brillouin zone are obtained. In the bond operator mean-field theory, it is found that a large number of triplet modes are non-dispersive. In particular, the lowest triplet excitation is non-dispersive and degenerate with a dispersive mode at the zone center. Away from the zone center, the lowest triplet is separated from two other flat modes by a small energy gap. Quantum fluctuations are considered by taking into account scattering processes of two triplets and their bound state formation, which leads to a downward renormalization of the lowest spin triplet gap. The dispersion of the lowest triplet excitation in the VBS state is compared with the dispersive lower bound of the triplet continuum expected in competing spin liquid phases. Implications to future neutron scattering experiments are discussed.