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.

我们的目标是解决相关电子系统中的微观机制。为了能够以空间分辨率记录数据，我们将使用一台多功能的自制变温扫描力显微镜进行以下项目。主要研究目标是阐明二氧化钒(VO2)中金属-绝缘体转变的机制。在室温附近，VO2经历了一个相变，电导率变化高达5个数量级，晶胞倍增。对VO2的基本兴趣源于迫切需要在如此多的前沿材料中了解Mott转变，而VO2？S罕见地被认为是在可接触的温度和压力下高度关联的Mott系统。此外，最近的新应用(如记忆电阻、超材料)的想法使VO2再次走到了技术的前沿。我们将解决一些大量研究无法解决的问题，例如在什么条件下可以实现电子跃迁和结构跃迁的分离。关联电子系统应用物理的第二个项目是直接测量超导体中的单涡钉扎力。涡旋运动导致了不必要的耗散，并对超导器件的临界电流Jc施加了严格的限制。对新的铁基高T_c超导体的输运实验表明，一种强烈的本征钉扎机制，其来源尚不清楚。我们将使用扫描探针方法来研究这些钉扎机制。未来一个雄心勃勃的计划是使用磁力显微镜来操纵耦合的拓扑绝缘体-超导系统中的涡旋，从而编织它们附着的Majorana费米子。

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.