Deconfinement of spinons in frustrated spin systems: Spectral perspective

The confinement and deconfinement of spinons in the square-lattice antiferromagnetic J₁-J₂ Heisenberg model are elaborated by exploring the evolution of the whole excitation spectra with J₂, based on the spin cluster perturbation theory. We find that deconfined spin-1 /2 spinons beyond the conventional spin-1 magnons have already emerged partially even in the limit J₂=0 and develop with J₂, exhibiting as a continuum close to (π ,0 ) in the Brillouin zone. In the region near J₂=0.5 J₁ , the entire spectrum is characterized by a broad continuum in which all magnons are deconfined into spinons, whose ground state is attributed to a Z₂ quantum spin liquid with the aid of a variational-Monte-Carlo analysis. The spinon continua are also found in the stripe phase with J₂>0.6 J₁ . Our study provides spectroscopic evidences for the fractionalized excitations and quantum spin liquid and highlights the rising field to explore the exotic quantum phases from a perspective of excitation spectrum.