[PAST EVENT] Melissa R. Beebe: Physics Dissertation Defense
Abstract: Electron correlations are the root of many interesting phenomena in materials, including phase transitions such as superconductivity and insulator-to-metal transitions, which are of great interest both for scientific understanding and for various applications. Such phase transitions can often be tailored in thin films, in which the geometry of the material is limited in one dimension. By studying how the physical structure of a thin film affects its correlated electron response, it is possible to obtain useful insight into both the nature of the electron correlations present in the material and how to control them for various applications. Niobium, an elemental superconductor, has the highest critical temperature and lower critical field of the naturally-occurring superconductors, making it attractive for many applications, particularly in the SRF (superconducting radio frequency) community. Several niobium-based compounds are also superconductors of interest; while the bulk materials are fairly well-understood, there is still a great deal to learn regarding the effects of the microstructure of thin films of these materials on their superconducting properties. Another niobium compound, niobium dioxide, exhibits a phase transition from a room-temperature insulating state to a high-temperature metallic state. Such insulator-to-metal transitions are not well-understood, even in bulk, and there is a great deal of debate over the mechanism that drives them. Experimental studies on niobium dioxide thin films are still somewhat rare and thus have the potential to contribute a great deal to the understanding of the mechanisms behind the transition. This dissertation presents structure-property correlation studies on niobium and niobium compound superconducting thin films such as those discussed above, and also reports on the first experimental studies of the light-induced insulator-to-metal transition in niobium dioxide.
Bio: Melissa Beebe was born in Alexandria, VA, and grew up in Dumfries and Chesapeake, VA. At age five, she decided to become a clown, but ultimately realized that her fear of heights made understanding the physics of circus acts a better choice than performing them. She graduated cum laude from Old Dominion University in 2012 with a B.A. in Spanish Language and Literature and a B.S. in Physics with a minor in Mathematics. That fall, she entered William & Mary to pursue her Ph.D. In the fall of 2013, she joined Ale Lukaszew's research group, where she has studied the growth and properties of thin films of niobium and related compounds which exhibit electron correlations.