Thin-Film Synthesis and Characterization of Chalcogenides for Quantum and Topological Phenomena

Chalcogenide materials display a wide range of solid state phenomena, some of which are relevant for quantum and topological phenomena, including topological ground states, rich spin physics, and superconductivity. Thin-film synthesis of this materials class enables tuning of condensed matter properties using lattice strain and dimensional effects at surfaces and interfaces. It also facilitates the development of nanoscale devices for applications, and permits the integration of other functional materials via heterostructuring approaches, providing further opportunities for creating exotic quantum phases that result from proximity effects and quantum confinement. One obstacle to realizing these goals is a general lack of extremely high-quality thin films with very limited defects. For example, the synthesis of chalcogenide thin films is often accompanied by the formation of an inhomogeneous domain structure or stoichiometric imperfection, which can obscure novel quantum and topological states.<br/><br/>In this talk, we focus on the thin-film synthesis of chalcogenide materials by molecular beam epitaxy (MBE) and the application of characterization techniques to understand and control the structure-property relationships in thin film chalcogenides. The MBE technique allows precise stoichiometry control, film-thickness control at the sub-monolayer level, and kinetic control of defect formation. We describe advances in MBE techniques that enable epitaxial growth of chalcogenide thin films with atomically flat surfaces and interfaces, followed by a description of topological and electronic properties. We also introduce the possibility of inducing picoscale structural distortions and changing local stoichiometry at surfaces and interfaces, focusing on the effect of structural distortions by the substrate on electronic correlations and macroscopic quantum transport. The investigation of such effects requires methods of measuring electronic and physical structures that are sensitive to surface and buried interfaces, representing another challenge to investigating novel quantum phases of chalcogenide thin films. An iterative feedback approach, which combines synthesis with monolayer precision and high-resolution characterization techniques, provides new insights into novel quantum phases that arise in this class of materials.