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Epitaxial thin-film growth provides a unique platform for exploring crystalline phases and physical properties that are difficult, or sometimes impossible, to access in bulk materials. By coupling a epitaxial stabilization on a single-crystal substrate, it can modify lattice strain, symmetry, dimensionality, and interfacial structure. These constraints can reshape the free energy landscape of a material and provide pathways toward metastable structures and emergent physical properties.
In this talk, I will discuss how epitaxial growth can be used not only as a synthesis technique, but also as a tool for exploring the relationship between crystal structure and materials physics. I will first present several examples from complex oxide thin films in which epitaxial constraints enable unusual electronic and structural states, including high-mobility two-dimensional electron systems in perovskite stannate heterostructures, strain-stabilized superconductivity in RuO2, and the epitaxial realization of the topological crystalline insulator Sr3SnO. Together, these examples illustrate how control of strain, interfaces, symmetry, and growth conditions can provide access to material states beyond those conventionally available in bulk equilibrium synthesis. I will then discuss our recent efforts to extend this approach from controlling known materials toward discovering materials in less-explored chemical spaces. Using suboxide molecular-beam epitaxy, we investigate the Sr–Ge–O system and find that its structural landscape is strongly influenced by growth conditions and substrate symmetry. Changes in the Sr/GeO flux ratio, substrate temperature, and substrate choice produce distinct epitaxial growth modes and crystal structures, including phases that are not represented in existing materials databases.
These results point toward a broader role for epitaxy in materials research, rather than simply reproducing known compounds in thin-film form, epitaxial growth can provide a controlled non-equilibrium environment for navigating complex energy landscapes, discovering previously unexplored crystalline phases, and connecting their atomic structure to emergent physical properties.