Tunable Mott Variable-Range Hopping in Sr₂IrO₄ Epitaxial Thin Films by Misfit Strain and Isovalent Doping

The J_eff = 1/2 Mott insulator Sr₂IrO₄ has attracted attention due to its novel electronic states originating from coexisting strong spin-orbit interaction and electron correlation. The similar magnetic and structural properties of Sr₂IrO₄ to layered cuprates has led to theoretical predictions of new superconducting states. Indeed, the d-wave gap symmetry has been observed with surface-electron doping. However, no superconducting transport property has been discovered in this compound so far.

We report three-dimensional Mott variable-range hopping (3D Mott-VRH) transport of Sr₂IrO₄ epitaxial thin films, analogous to other transition-metal oxide Mott insulators. However, the characteristic temperature of the 3D Mott-VRH varies under misfit strain or isovalent doping, implying that the density of states near the Fermi energy is reconstructed. Magneto-transport data indicates that the transport mechanism is governed by a disorder induced localization and electron-electron correlations. We will discuss the Mott VRH transport in Sr₂IrO₄ thin films in comparison with other Mott insulators such as La₂CuO₄ and LaMnO₃.