Metallicity in Ultrathin IrO₂ Thin Films through Heterostructure Engineering

Studying the intrinsic properties of thin film quantum materials is often limited by defects, particularly in the few monolayer regime where interfaces play a significant role. Here, using hybrid molecular beam epitaxy (MBE), we demonstrate single crystalline, epitaxial TiO₂/IrO₂/TiO₂ (110) heterostructures with precisely engineered interfaces that result in improved film quality, particularly evidenced by an evolution to well-defined streaky reflection high energy electron diffraction (RHEED) patterns. The improved film quality in these heterostructures further led to the realization of metallicity in IrO₂ down to 2 monolayers (~ 6.4 Å) film thickness. We also observed anisotropic in-plane resistivity driven largely by an anisotropy in carrier mobility. The IrO₂ films also showed some of the lowest room-temperature resistivities reported in ultrathin films, enabling new understanding of resistivity scaling in ultrathin metals.