Physics & Astronomy Colloquium

3:30 PM, Friday, February 6, 2009
Room 137, Chem-Phys Building

Dr. Robert Cava
Department of Chemistry
Princeton University

Insulator to Correlated-Metal Transition in doped VO2
Materials that should be metallic conductors by simple electron counting and yet are electrical insulators have been of interest for decades as embodiments of strong electron-electron and electron-lattice interactions in solids. Among the most iconic of such materials is Rutile structure VO2, a 3d1 compound whose crystal structure is based on chains of edge-sharing VO6 octahedra. VO2 undergoes a structural distortion that creates V-V pairs along the chains when it is cooled through its metal to insulator transition. The V-V pairs localize the 3d1 electrons in spin singlets. First addressed in the 1970s, the current understanding is that neither of the most common scenarios - the Mott state, in which Coulombic repulsion between electrons attempting to occupy the same site introduces an energy gap, or the Peierls state, in which electrons on neighboring sites form localized spin singlets and metal-metal pairs - is alone sufficient to explain VO2's electronic properties. In this talk, I will describe the electronic and magnetic properties of the V1-xMoxO2 solid solution. The Mo doping of VO2, which introduces electrons, first results in the formation of localized magnetic states, due to breaking up the spin singlets and releasing their moments. These localized states then hybridize on continued doping to form an intermediate mass metal with substantial remnant magnetic character. The results will be discussed in the context of the literature on metal-insulator transitions in solids.

Refreshments will be served in CP 139 at 3:15 PM