Two-Dimensional Synthetic Quantum Matter

Stanford University, Stanford CA

Investigators

Abstract

Non-technical abstract. The ways in which electrons move through different types of materials provide the foundations for nearly all modern electronic technology. For example, the electron flow through the semiconductor silicon can be turned on or off, or modulated like a valve, and these behaviors are the basis behind transistors, computer processors, and all electronic communication. To maintain continued progress in electronics technology, the underlying components and materials must be continuously scaled down in size. However, this progress is now stymied by the fact that critical dimensions are approaching "quantum" sizes where the position of even a single stray atom or molecule plays a measurable role in performance, and the flow of electrons is impeded by atom-size impurities and even by their own tiny weight. New materials hold the key to circumventing many of these problems, but new materials are often difficult to understand and therefore apply, due to their complex nature. This project synthesizes new electronic materials using one of the most advanced laboratory technologies available-the controlled manipulation of single atoms and molecules to build up from scratch entirely new materials that can guide electrons in ways not possible with existing materials. These new materials are built one atom at a time as a means to test how new fundamental physics can be applied to electronic technologies, such as making electrons move as if they have no weight, and making electron avoid obstacles so that their flow through electronic devices is unimpeded. The information learned from these studies feeds back into synthesizing larger versions of the same materials in bulk. In the process of conducting the calculations and experiments of this project, Ph.D. students receive education and training in the critical fields of nanotechnology and nanomaterials, and undergraduate students receive exposure to state-of-the-art research. The research team teaches courses into which current research in nanoscale science and technology is interwoven, manages a program that hosts and mentors visiting students from underrepresented-minority-serving community colleges in 10-week lab research internships, and actively makes available nanoscience educational tools and multimedia for the general public. Technical abstract. This project applies atomic and molecular manipulation to the nanoscale assembly of novel quantum materials-materials whose structural and electronic properties are dominated by quantum mechanics and give rise to either novel behavior or promising technologies. The primary experimental apparatus for these investigations are custom-built low-temperature scanning probe microscopes capable of both studying and controlling matter at atomic length scales. Beyond these tools, methods and approaches also involve tools of theoretical quantum design, developed synergistically with experiments. The overall project goal is to create synthetic two-dimensional nanomaterials exhibiting new properties and states of matter not possible in their natural-materials counterparts. The scope of this project targets exquisite control of internal quantum degrees of freedom-such as electron amplitude and phase engineering through local bond-length manipulation-to enable new electronic behavior sought in modern science and technology. Work focuses on two-dimensional materials and strain-engineered phases, involving variants of Dirac materials such as graphene and the related dichalcogenide honeycomb structure molybdenum disulfide. Local probes and application of these materials are at the forefront of experimental studies and are relevant to a burgeoning class of new designer materials. Specific experiments include: using atomic-scale strain texturing to embed pseudoelectric and pseudomagnetic gauge fields into artificial molecular graphene, and pseudoelectric fields within "artificial atoms" of other strained two-dimensional monolayers; structure and atomic manipulation of boundary states and topological confinement within the same materials; assembly of electron quasicrystals and non-periodic matter.