Scanning probe microscopy and correlated electron physics: spatial imaging and manipulation of novel materials including the metal-insulator and structural phase transitions in Vanadium dioxide.

• Applicant: Dr. Magdalena Huefner
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2011 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 202347482

We aim to address microscopic mechanisms in correlated electron systems. In order to be able to record data with a spatial resolution we will employ a versatile, homebuilt, variable temperature scanning force microscope to work on the following projects.The primary research objective is to elucidate the mechanism of the metal-insulator transition in vanadium dioxide (VO2). Near room temperature, VO2 undergoes a phase transition with up to 5 orders of magnitude change in conductivity, and a doubling of the crystal unit cell. Fundamental interest in VO2 stems from the urgency of understanding the Mott transition in so many forefront materials, and VO2¿s rarity as a highly correlated Mott system at accessible temperatures and pressures. Furthermore, recent ideas for new applications (e.g. memristors, metamaterials) have brought VO2 to the technological forefront again. We will address a number of questions which cannot be addressed with bulk studies, such as the conditions under which separation of electronic and structural transitions may be achieved.A second project in the applied physics of correlated electron systems is to directly measure single vortex pinning forces in superconductors. Vortex motion leads to undesired dissipation and places severe limits on the critical current Jc in superconducting devices. Transport experiments on the new iron-based high-Tc superconductors suggest a strong native pinning mechanism, of yet unknown origin. We will investigate these pinning mechanisms using scanning probe methods.An ambitious future project, which evolves logically from the proposed high-Tc vortex pinning project, is to use a magnetic force microscope to manipulate vortices in a coupled topological insulator ¿ superconductor system, and therefore braid their attached Majorana fermions.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professorin Dr. Jennifer Hoffman