Capturing and controlling antiferromagnetic fluctuations of pseudospin-half square lattice in artificial layered iridate.

Increasing attention has been paid to 5d transitional metal compounds due to the intriguing impacts of spin-orbit coupling (SOC) and the possibilities of obtaining unique emergent properties. However, as one of the most important systems, the square-lattice iridates that can be described by a pseudospin-half Hubbard model show remarkable similarities to the parent compound of weakly spin-orbit-coupled high-Tc cuprates. The hidden role of strong SOC for correlated pseudospin-half electrons remains elusive, partly because of the limited available compounds with the Ruddlesden-Popper structure. This material bottleneck can be overcome by synthesizing and tailoring pseudospin-half square lattices in artificial layered structures. I will discuss our recent investigation on artificial crystal Sr_n+mIr_nTi_mO_3n+3m synthesized as perovskite (SrIrO₃)_n/(SrTiO₃)_m superlattices, which not only replicate the magnetic state and excitations but also afford remarkable tunabilities beyond the Ruddlesden-Popper phases, demonstrating the extraordinary sensitivity of the pseudospin-half electron to the structural modulations implemented by design. In virtue of this structural control, we are able to realize toy-model systems where the SOC is utilized to capture the two-dimensional fluctuations predicted by the Mermin-Wagner theorem as a giant enhancement of the antiferromagnetic ordering temperature under uniform magnetic field. Emergent longitudinal spin fluctuations characteristics of the Slater-Mott crossover are also observed as positive anomalous magnetoresistance above the ordering temperature. The results showcase that the SOC of 5d electrons provides potent pathways to capture the physics underlying correlated systems.