James C. McGroddy Prize for New Materials (2021): Breaking the Rules to Unleash Novel Phenomena in Oxides

When it comes to unleashing hidden ground states in oxides and the novel phenomena they possess,
oxide molecular-beam epitaxy (MBE) rocks! In this talk I will highlight a few examples from the past >30 years of oxide MBE demonstrating how the atomic-layer control made possible by this technique can be used to break synthesis rules and create metastable compounds and heterostructures with intreguing ground states. Examples include the use of strain engineering, interface engineering, epitaxial stabilization, or dimensional confinement to transmute materials from ground states that are “vegetables” into ground states that are ferroelectric, ferromagnetic, both at the same time (multiferroic), or superconducting. A key element of this modern alchemy is the availability of underlying substrates with appropriate structural motifs to strain these complex oxide thin films to percent levels—far beyond where they would crack or plastically deform in bulk—or to stabilize metastable polymorphs. The effects of this epitaxial engineering on the band structure of these oxide heterostructures is revealed by high-resolution angle-resolved photoemission (ARPES) on pristine as- grown surfaces of these complex oxides made possible by a direct ultra-high vacuum connection between the MBE and ARPES.

* The work reported was performed in collaboration with superb students, postdocs, colleagues, and collaborators
from around the world.