Spinon confinement in a quasi-one-dimensional XXZ Heisenberg antiferromagnet.

Half-integer spin Heisenberg chains constitute a key paradigm for quantum number fractionalization: flipping a spin creates a minimum of two elementary spinon excitations. These have been observed in numerous experiments. We report on inelastic neutron scattering experiments on the quasi-one-dimensional anisotropic spin-1/2 Heisenberg antiferromagnet SrCo$_{2}$V$_{2}$O$_{8}$. These reveal a mechanism for temperature-induced spinon confinement, manifesting itself in the formation of sequences of spinon bound states. A theoretical description of this effect is achieved by a combination of analytical and numerical methods.