Two-dimensional ${J}_{ m eff}$ = 1/2 antiferromagnetic insulator unraveled from interlayer exchange coupling in artificial perovskite iridate superlattices

摘要

We report an experimental investigation of the two-dimensional ${J}_{\rmeff}$ = 1/2 antiferromagnetic Mott insulator by varying the interlayer exchangecoupling in [(SrIrO$_3$)$_1$, (SrTiO$_3$)$_m$] ($m$ = 1, 2 and 3)superlattices. Although all samples exhibited an insulating ground state withlong-range magnetic order, temperature-dependent resistivity measurementsshowed a stronger insulating behavior in the $m$ = 2 and $m$ = 3 samples thanthe $m$ = 1 sample which displayed a clear kink at the magnetic transition.This difference indicates that the blocking effect of the excessive SrTiO$_3$layer enhances the effective electron-electron correlation and strengthens theMott phase. The significant reduction of the Neel temperature from 150 K for$m$ = 1 to 40 K for $m$ = 2 demonstrates that the long-range order stability inthe former is boosted by a substantial interlayer exchange coupling. Resonantx-ray magnetic scattering revealed that the interlayer exchange coupling has aswitchable sign, depending on the SrTiO$_3$ layer number $m$, for maintainingcanting-induced weak ferromagnetism. The nearly unaltered transitiontemperature between the $m$ = 2 and the $m$ = 3 demonstrated that we haverealized a two-dimensional antiferromagnet at finite temperatures withdiminishing interlayer exchange coupling.