Confinementr and deconfinement of topological excitations in Na$_{2}$IrO$_{3}$

Using phase sensitive heterodyne transient grating technique we establish that in the limit of low pumping fluences the optical response of Na-213 iridate system below the antiferromagnetic ordering temperature T$_{\mathrm{N}}$ is dominated by Hubbard excitons (HE). Unpaired single particle excitations (SE) constituting HE are strongly suppressed, appearing only above T$_{\mathrm{N}}$. We argue that this is due to the interplay between the frustrated Kitaev term in the Hamiltonian and the weak Heisenberg term responsible for the antiferromagnetic order below T$_{\mathrm{N}}$, which mediates an effective interaction between spin singlet SE excitations. This interaction grows linearly with distance resulting in a sudden increase of the exciton binding energy as the system enters the ordered state. This is a solid state realization of a phenomenon known in high energy physics as confinement.