Condensed-Matter Physics & Materials Science Seminar

The phenomenon of metal-insulator phase transition in strongly correlated electron systems is one of the focus areas of research in condensed matter physics. The interest is partly motivated by the potential of the materials exhibiting a metal-insulator transition to be used in novel electronics and electro-optic applications as switches or memory elements. There is also considerable interest in understanding the fundamental science behind the correlated electron behavior responsible for striking material property changes such as high temperature superconductivity, metal-insulator transition, and colossal magnetoresistance. Vanadium dioxide has received special attention because of the substantial scale of the metal-insulator transition in this material, the fact that the transition temperature is near room temperature (67˚C), and extremely fast optical switching upon the transition (~100 fs).

I will present the results of our study of the energy band structure of vanadium dioxide (VO2) thin films by means of x-ray absorption and photoemission spectroscopy across the metal-insulator transition (MIT). The results are related to the electron transport parameters, stoichiometry, and morphology of the films. The analysis allows us to conclude on the importance of the electron correlations, details of the atomic coordination changes in the material for different film morphologies and across MIT, and the nature of electron transport. The optical studies of VO2 films provided the evidence of the percolative nature of the phase transition and revealed record high switching of the mid-infrared reflectance upon MIT. Our recent Hall effect experiments allowed determining the carrier density and electron mobility across the MIT – important parameters in the Mott theory of MIT. Possible applications in electronics and our current experiments with VO2 devices will be outlined.