Deconfinement of spinons in frustrated spin systems: Spectral perspective

The confinement and deconfinement of spinons in the square-lattice antiferromagnetic J(1)-J(2) Heisenberg model are elaborated by exploring the evolution of the whole excitation spectra with J(2), 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 J(2) = 0 and develop with J(2), exhibiting as a continuum close to (pi, 0) in the Brillouin zone. In the region near J(2) = 0.5 J(1), the entire spectrum is characterized by a broad continuum in which all magnons are deconfined into spinons, whose ground state is attributed to a Z(2) quantum spin liquid with the aid of a variational-Monte-Carlo analysis. The spinon continua are also found in the stripe phase with J(2) > 0.6 J(1). 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.