Heterostructures Grown by Metalorganic MBE*

Emergent phenomena in complex oxide heterostructures can be tuned by the choice of ions from the 3d, 4d, and 5d blocks of the periodic table to produce a wide array of properties. These can include superconductivity, ferromagnetism, topological states, and ferroelectricity all within a single class of materials. Such phenomena provide rich opportunities for engineering of unusual combinations of behavior through the design of multi-layer thin films. Our work employs hybrid metal-organic MBE and in vacuo X-ray photoelectron spectroscopy (XPS) to explore oxide films that exhibit strong spin-orbit coupling and interfacial charge transfer. Such materials have traditionally been difficult to synthesize via MBE because of the refractory nature of 4d and 5d transition metals. Thus far, we have demonstrated hard-to-grow materials comprised of refractory 4d and 5d cations, including SrNbO₃, SrIrO₃, and SrHfO₃.

Our work presented in this talk focuses on SrIrO₃ heterostructures grown using an iridium acetylacetonate solid source grown from an effusion cell. We have synthesized epitaxial films under different thickness and strain conditions and examined the role that these play on the electronic transport and carrier dynamics. We show that the metallicity can be tuned via increasing compressive strain and employ time-domain THz spectroscopy to examine the origins of this behavior. We have also explored heterostructures and superlattices that focus on tuning the Fermi level in SrIrO₃ through interfacial charge transfer. This work is performed using SrNbO₃ as an n-type interfacial donor and SrCoO₃ as a ferromagnetic p-type interfacial acceptor. We show transport studies on both systems as well as spectroscopic examination of Ir valence states to probe how the Fermi surface of semimetallic SrIrO₃ can be tuned.