We report an experimental investigation of the two-dimensional $J_{\text{eff}}=1/2$ antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [${({\mathrm{SrIrO}}_3)}_1$, ${({\mathrm{SrTiO}}_3)}_m$] ($m=1$, 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the $m=2$ and $m=3$ samples than the $m=1$ sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive ${\mathrm{SrTiO}}_3$ layer enhances the effective electron-electron correlation and strengthens the Mott phase. The significant reduction of the Néel temperature from 150 K for $m=1$ to 40 K for $m=2$ demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the ${\mathrm{SrTiO}}_3$ layer number $m$, for maintaining canting-induced weak ferromagnetism. The nearly unaltered transition temperature between the $m=2$ and the $m=3$ demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.

• Received 29 January 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.027204