EAPSI: Fundamental experimental materials physics for next generation electronics devices

摩尔定律描述了晶体管性能的惊人增长，晶体管是计算机的基本组成部分，它正在接近可伸缩性和性能的基本量子极限。这些最小尺寸和最快速度的硬限制恰逢电子产品需求爆炸式增长的同时，从手机到支撑互联网的数据中心，以及为这些基础设施发电而产生的环境后果。一种可能的解决方案是开发一种基于完全不同的物理原理的替代晶体管：在传统的电压调制的基础上操纵电子的自旋态。在过去的十年里，一个令人兴奋的凝聚态物理的新领域--拓扑绝缘体，在理论上假设并实验上实现了一类在电子自旋和动量之间具有非平凡关系的材料。这两种特性之间的这种关键耦合可能是现有电子产品范例与未来实现更快、更节能设备之间的联系。然而，目前实现这些特性的材料在环境条件下仍然远远不牢固，这不仅仅是一种科学上的好奇心。为了更好地了解这些现有材料的局限性，这个项目利用了东京大学固态物理研究所长谷川幸男教授的实验室提供的一种实验技术，称为自旋极化扫描隧道显微镜(SP-STM)，能够以原子尺度的空间分辨率测量电子的自旋态。SP-STM是一种特别适合这一背景的实验技术；由于其表面敏感和原子分辨，允许直接观察理论预测的拓扑保护如何在缺陷位置散射中表现出来。作为目前最有前途的拓扑绝缘体，硒化铋的晶体结构和力学性能使得扫描隧道显微镜样品的表面制备相对容易。测量电子在散射点的离面自旋极化将澄清现有用于理解拓扑绝缘体的理论框架，并为如何利用自旋电子异质结中的表面态提供信息。该NSF EAPSI奖是与日本科学促进会合作资助的。

Moore's "law", describing the fantastic increase in performance of transistors, the fundamental building block of computers, is approaching fundamental quantum limits of scalability and performance. These hard limits of smallest size and fastest speed coincide with the explosion of demand for electronics, from phones to the data centers underpinning the internet, and the environmental consequences of generating the electricity to power this infrastructure. One possible solution is to develop an alternative transistor based on a completely different physics: manipulation of the spin state of an electron in place of conventional voltage modulation. Over the past decade, an exciting new field of condensed matter physics, topological insulators, has theoretically postulated and experimentally realized a class of materials possessing a non-trivial relationship between electron spin and momentum. This crucial coupling between the two properties could be the link between the existing paradigm of electronics and future realizations of faster, vastly more energy efficient devices. However the current materials in which these properties are realized remain far from robust in the environmental conditions required to be more than a scientific curiosity. To better understand these existing materials limitations, this project takes advantage of an experimental technique available at Professor Yukio Hasegawa's laboratory at the Institute of Solid State Physics, University of Tokyo, called spin-polarized scanning tunneling microscopy (SP-STM), capable of measuring the spin states of electrons with atomic scale spatial resolution.SP-STM is a particularly well-suited experimental technique within this context; being surface sensitive and atomically resolved allows for the direct observation of how the theoretically predicted topological protection manifests itself in scattering at defect sites. Bismuth selenide, the most promising topological insulator to date, has a crystal structure and mechanical properties making surface preparation of samples for STM relatively facile. Measuring the out of plane spin polarization of electrons at scattering sites will clarify the existing theoretical framework used to understand topological insulators, and inform how to utilize the surface states in spin electronic heterostructures. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.