Evidence of two-spinon bound states in the magnetic spectrum of Ba3CoSb2 O9

Abstract

Recent inelastic neutron scattering (INS) experiments of the triangular antiferromagnet Ba3CoSb2O9 revealed strong deviations from semiclassical theories. We demonstrate that key features of the INS data are well reproduced by a parton Schwinger boson theory beyond the saddle-point approximation. The measured magnon dispersion is well reproduced by the dispersion of two-spinon bound states (poles of the emergent gauge fields propagator), while the low-energy continuum scattering is reproduced by a quasifree two-spinon continuum, suggesting that a free spinon gas is a good initial framework to study magnetically ordered states near a quantum melting point.