Continuum of spin excitations in an ordered magnet

Spin excitation continua observed in neutron scattering studies are often considered to be strong evidence of quantum spin liquid formation. In a disorder-free magnetic compound with a quantum spin liquid ground state, the elementary excitation is no longer the conventional spin waves (magnons). Instead, the magnons fractionalize into spinons, producing a characteristic two-spinon continuum. However, it remained uncertain whether a clean, ordered antiferromagnet could exhibit a continuous spectrum similar to that of a quantum spin liquid. This paper presents evidence of a spin excitation continuum in the magnetically ordered state of Na 2 BaCo(PO 4 ) 2 , where free spinons are absent. This challenges the interpretation of such a continuum as a definitive signature of a quantum spin liquid in new material studies.