Physics (Internal)

Growth and X-Ray Spectroscopy Studies of Correlated Vanadium Oxides

This event is part of the Preliminary Oral Exam.

Examining Committee:  Kevin Smith, Richard Averitt, Linda Doerrer, Xi Lin, Scott Whitaker   Abstract: The electronic structure of correlated electron systems has been one of the most interesting topics in condensed matter physics, due to their complex and fascinating properties along with technological applications. Vanadium oxides are prototypical correlated materials, which show the rich properties of metal-insulator transition (MIT), as well as charge ordering transitions, structural and magnetic phase transitions. The vanadium-oxide samples in this study are synthesized by different techniques of crystal growth, sol-gel process, and vacuum deposition to obtain various forms of single crystals, polycrystalline and epitaxial films with doping. Our experimental tools of measuring the electronic structure are synchrotron-based x-ray spectroscopies, including soft x-ray emission spectroscopy (XES), soft x-ray absorption spectroscopy (XAS), resonant inelastic soft x-ray scattering (RIXS), x-ray photoemission spectroscopy (XPS), and angle resolved photoemission spectroscopy (ARPES). The XAS, XES, and XPS study on the electronic structure of Na_xV₂O₅ (x ~ 0.33) polycrystalline films has shown good β-phase crystal structure with Na doping, which is promising for displaying the property of MIT with charge ordering in the future study. To test theories about the orbital ordering in rare-earth vanadates, RVO₃, with varied rare-earth ionic sizes during phase transitions as temperature changes, V L-edge RIXS has been applied to probe the O 2p-V 3d charge transfer excitations and V 3d-3d transitions in Lu_1-xLa_xVO₃ single crystals.