Probing the Influence of Magnetism and Superconductivity on Topological Insulators & their Surface States

技术摘要：拓扑绝缘体是一类新的绝缘体，它的自旋-轨道相互作用如此强烈，以至于绝缘能隙被反转，在能隙上方本应出现的高能状态实际上出现在能隙之下。这种能带反转的一个关键结果是出现了对无序和化学势变化的影响很强的拓扑表面态，使它们在未来的电子应用中引起了强烈的兴趣。虽然在理论和实验方面的快速发展使拓扑绝缘体成为密集研究的主题，但以前的工作主要集中在它们的电子性质上。本项目致力于了解拓扑绝缘体及其表面态的下一个前沿，阐明磁性和超导电性对其物理特性和电子行为的影响。磁场的应用有望成为一种强有力的方法来调制拓扑表面态的性质，并预测磁诱导的带隙拓扑表面态将产生一系列奇异的磁光和电子输运效应。当地的光谱技术和PI最先进的扫描隧道显微镜(STM)设施将允许对这些效应进行纳米级的检查。非技术摘要：在发现量子力学后不久，人们就意识到为什么有些固体是绝缘的(如钻石)，而另一些固体是高导电的(如石墨)，尽管它们可以由相同的元素组成。80年后的今天，绝缘体和金属的概念再次发生了根本性的改变。在过去的几年里，很明显，可以有一种不同类型的绝缘体，这可能是因为由较重元素组成的材料中的电子波函数的拓扑结构所致。这些化合物中电子的自旋和轨道角动量之间的强相互作用改变了它们电子态的能量顺序。这种拓扑特征的关键结果(以及区分拓扑绝缘体和普通绝缘体的方法)是在它们的表面存在具有螺旋自旋织构的金属电子。所提出的程序将直接可视化这些新的物质量子态，并通过扫描隧道显微镜(STM)的光谱映射来展示它们的异常性质。作为拟议计划的一部分，这些新的量子态在电子应用中的潜力将被研究。作为该计划的一部分，本科生、研究生和博士后研究人员将接受培训。

Technical Abstract: Topological insulators are a new class of insulators in which spin-orbit interactions are so strong that the insulating energy gap is inverted, the states that should appear at high energy above the gap actually appear below the gap. A key consequence of this band inversion is the appearance of topological surface states that are robust to the effects of disorder and changes in the chemical potential, making them of strong interest for future electronics applications. While rapid developments on both theoretical and experimental fronts have made topological insulators the subject of intense study, previous work has focused on their electronic properties. This project addresses the next frontiers of understanding topological insulators and their surface states, elucidating the influence of magnetism and superconductivity on their physical characteristics and electronic behavior. The application of magnetic fields is expected to be a powerful method by which the properties of topological surface states could be modulated, and magnetism-induced gapped topological surface states are predicted to give rise to a number of exotic magneto-optical and electron transport effects. Local spectroscopic techniques and the PI's state-of-the-art scanning tunneling microscope (STM) facilities will allow nanometer-scale examination of these effects. Non-technical Abstract: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 wavefunctions in materials comprised of heavier elements. Strong interaction between the spin and the orbital angular momentum of electrons in these compounds alters the sequence in energy of their electronic states. 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. The proposed program will directly visualize these novel quantum states of matter and demonstrate their unusual properties through spectroscopic mapping with the scanning tunneling microscope (STM). The potential of these novel quantum states for electronic application will be examined as part of the proposed program. Undergraduate, graduate, and postdoctoral researchers will be trained as part of the program.