Fractionalized spin-wave continuum in kagome spin liquids

With strong quantum fluctuations and geometry frustrations, spin systems may achieve quantum paramagnetic ground states which are called quantum spin liquid states. Such spin liquids are characterized by long range many-body entanglement and symmetries (e.g. spin-rotation symmetry and crystal symmetries) may be fractionalized. In Herbertsmithite [ZnCu3(OH)6Cl2] (a layered kagome antiferromagnet), fractionalized spin-wave continuum (SWC) has been observed in recent neutron scattering measurement. Motivated by the experiment,  we use Gutzwiller-projected wave functions to study dynamic spin structure factor of spin liquid states on the kagome lattice. Three different spin liquid candidates, spinon Fermi-surface spin liquid (FSL), Dirac spin liquid (DSL) and random-flux spin liquid (RSL), are investigated.  We find that there is no obvious contradiction between DSL and neutron scattering measurements. Besides a fractionalized spin ( i.e. spin-1/2), spinons in DSL carry a fractionalized crystal momentum which is potentially detectable in SWC in the neutron scattering measurements. Based on LDA calculations, we also propose selective doping Barlowite varieties (Cu3Mg(OH)6FBr and Cu3Zn(OH)6FBr)  as promising new kagome materials with much less imperfection.