“Visualizing and Manipulating Topological Quantum States in Novel Materials and Nanostructures”
Soon after the discovery of quantum mechanics it was realized why some solids are insulating (like diamond) and others are highly conducting (like graphite), even though they could be comprised of the same element. Now, 80 years later, the concept of insulators and metals is again being fundamentally revised. During the last few years, it has become apparent that there can be a distinct type of insulator, which can occur because of the topology of electronic wave functions in materials. The key consequence of this topological characteristic (and the way to distinguish a topological insulator from an ordinary one) is the presence of metallic electrons with helical spin texture at their surfaces. I will describe experiments that directly visualize these novel quantum states of matter and demonstrate their unusual properties through spectroscopic mapping with the scanning tunneling microscope (STM). These experiments show that the spin texture of these states protects them against back scattering and localization. In fact, these states appear to penetrate through barriers that stop other electronic states. I will also describe more ongoing efforts focused on manipulating these states with magnetism and experiments on new class of topological states that are protected by crystalline symmetry. Finally, I will describe efforts in which atomically fabricated nano structures are being used to create new class of topological states involving superconductors and the hunt for novel topological edge modes that behave like Majorana Fermions.
Refreshments at 3:30pm in 4-349 (Pappalardo Community Room)