Exotic Magnetic Properties In Strain-Modulated Slater-Mott Crossover Regime

Novel states and emergent phenomena arising from the interplay of charge, spin, and structural degree of freedoms in complex oxides are of particular interest in both fundamental physics and engineering application. Recent developments in 5d transition metal oxides, which have a strong spin-orbital coupling and an intermediate electronic correlation, have unraveled various exotic phenomena that are rarely observed or absent in 3d transition metal oxides. One of the prominent examples is the pseudospin-½ square lattice in iridates that can simulate the 2D single-orbital Hubbard Hamiltonian with a hidden SU(2) symmetry in the Slater-Mott crossover regime, in contrast to the strong antiferromagnetic (AFM) Mott insulating state in 3d transition metal oxides. By creating artificial superlattice of the pseudospin-½ square lattice, we are able to capture the anomalous transport behavior in this crossover regime. We have also achieved modulating the correlation strength of the pseudospin-1/2 electronic state across this regime by applying epitaxial strain and directly probing the AFM order parameter in these ultrathin samples. Moreover, combined dimensionality-control and site dilution over the superlattice, we have observed emergent isotropic spin fluctuations despite the planar anisotropy of the square lattice. This enhanced fluctuation enables giant responses of the AFM order to the external magnetic field. Our work has shown that pseudospin-1/2 iridate superlattice is a powerful platform to study correlation physics as well as realize function controls.