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的微观机制。为了能够以空间分辨率记录数据，我们将采用一种通用的，自制的，可变温度扫描力显微镜来进行以下项目。主要研究目的是阐明二氧化钒（VO2）中金属-绝缘体转变的机理。在室温附近，VO2经历了相变，电导率变化高达5个数量级，晶体单位胞加倍。对VO2的根本兴趣源于理解这么多前沿材料中的Mott转变的紧迫性，以及VO2在可访问的温度和压力下作为高度相关的Mott系统的稀有性。此外，新应用（如忆阻器、超材料）的最新想法再次将VO2带到了技术前沿。我们将解决大量研究无法解决的一些问题，例如电子和结构跃迁分离可能实现的条件。相关电子系统应用物理学的第二个项目是直接测量超导体中的单涡旋钉住力。涡旋运动导致不希望的耗散，并严重限制了超导器件的临界电流Jc。对新型铁基高tc超导体的输运实验表明，一种强大的原生钉住机制，但起源未知。我们将使用扫描探针方法来研究这些钉钉机制。一个雄心勃勃的未来项目，从提出的高tc涡旋固定项目逻辑发展而来，是使用磁力显微镜来操纵耦合拓扑绝缘体-超导体系统中的涡旋，从而编织它们附着的马约拉纳费米子。

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.