Materials World Network: Project Summary Disorder Tuned Quantum Phases in Topological Insulators

在过去的几年里，材料科学有了爆炸性的发展。它首先从理论上预测了一种新型的三维（3D）拓扑绝缘体（ti），这种绝缘体是完全间隙的，并且具有不寻常的无间隙保护的二维狄拉克表面态。这种保护来自线性能量-动量色散，费米表面附近的表面态驻留在单个狄拉克锥上。如果实现，这些系统可能是自旋电子学和容错量子计算领域的圣杯。然而，获得这种二维量子物质是一个挑战，因为很难将表面贡献与体的有限电导率分开。在这个由材料研究部支持的MWN项目中，快速（~ MeV范围）的电子和/或质子束将通过(a)调整Dirac点上的散体载流子密度和费米能级，以及(b)通过强迫安德森局域化来降低散体电导率，从而产生可控的无序。前者将导致大量TI中的电荷补偿。后者将测试量子化反常霍尔效应（QAHE）的最新理论思想，甚至更值得注意的是，(c)测试最近对拓扑安德森绝缘体的预测-通过在具有强自旋轨道相互作用的金属中引入无序而获得的具有量子化电导的非寻常量子相。确定发生这种情况的精确剂量应该为实现拓扑表面态的本征量子输运建立一个新的大规模途径。非技术总结：控制材料量子力学特性的能力是材料科学家和凝聚态物理学家面临的前沿挑战之一。在过去的几十年里，为了实现这一目标，人们设计了几种自下而上的方法，力求在原子水平上设计新材料（从而控制它们的性质）。在本提案中，将采用自上而下的材料修改方法，其中将引入控制数量的缺陷来改变拓扑绝缘体（TI）的电性能-这是一种新发现的材料，有望为量子计算提供强大的平台。由于粒子辐照引入的TI无序的独特性质只会影响这些材料的不需要的/寄生的电学性质，同时增强所需的量子性质，这将促进实现革命性的电子设备和新物质状态的合成。该提案是纽约城市学院(CCNY) - CUNY PI的凝聚态物理小组与法国Palaiseau ecol<s:1>理工学院的小组之间的国际合作，他们在快速粒子辐照技术和先进光谱学方面具有独特的专业知识。此次合作将材料科学的互补技术优势与粒子束技术相结合，以控制和调整新发现的功能材料类的关键电子特性。CCNY是联邦政府认可的少数民族服务机构。巴黎综合理工学院是法国领先的高等教育机构之一，具有明确的国际视野。该研究项目将对参与的研究生和本科生产生巨大的教育影响，因为它将促进国际访问和交流，扩大他们的教育范围，并在合作精神下提供广泛的材料合成和实验表征技术方面的培训。

TECHNICAL SUMMARY:In the last few years there has been an explosive development in materials science. It began with the theoretical prediction of a new class of three dimensional (3D) topological insulators (TIs) which are fully gapped in the bulk, and with unusual gapless protected 2D Dirac surface states. This protection arises from the linear energy-momentum dispersion, with the surface states near the Fermi surface residing on a single Dirac cone. If realized, these systems could be the Holy Grail in the fields of spintronics and fault-tolerant quantum computing. However, access to this 2D quantum matter is a challenge, owing to the difficulty of separating surface contribution from the finite conductivity of the bulk. In this MWN project supported by the Division of Materials Research, swift (~ MeV range) electron and / or proton beams will be utilized to create controlled disorder by (a) tuning the bulk carrier density and Fermi level across the Dirac point, and (b) reducing bulk conductivity by forcing Anderson localization. The former will result in charge compensation in a bulk TI. The later will test recent theoretical ideas of Quantized Anomalous Hall Effect (QAHE) and, even more remarkably, (c) test a recent prediction of a Topological Anderson Insulator - a nontrivial quantum phase with quantized conductance obtained by introducing disorder in a metal with strong spin-orbit interaction. Determining the precise dose at which this occurs should establish a new large-scale route to achieving intrinsic quantum transport of the topological surfaces states.NON-TECHNICAL SUMMARY:The ability to control the quantum mechanical properties of materials is one of the forefront challenges for material scientists and condensed matter physicists. In the past few decades several bottom-up approaches striving to engineer new materials (thereby controlling their properties) at the atomic level have been devised to achieve this goal. In this proposal a top-down material modification approach will be utilized in which a controlled amount of defects will be introduced to alter the electrical properties of topological insulators (TI's) - a newly discovered class of materials which promises to offer a robust platform for quantum computing. Owing to the unique properties of TI's disorder introduced by particle irradiation will only affect the unwanted / parasitic electrical properties of these materials, while simultaneously enhancing the desired quantum properties that will foster the realization of revolutionary electronic devices and the synthesis of novel states of matter. This proposal is an international collaboration between the condensed matter physics group of the PI at The City College of New York (CCNY) - CUNY, and groups at Ecolé Polytechnique in Palaiseau, France, with unique expertise in swift particle irradiation techniques and advanced optical spectroscopy. This collaboration combines the complementary technical strengths of materials science with particle beam technology to control and tune key electronic properties of the newly discovered functional materials class. CCNY is a federally recognized minority serving institution. Ecole Polytechnique is one of the leading institutes of higher education in France, with a decidedly international outlook. The research program will have a great educational impact on the students involved, both graduate and undergraduate, for it will facilitate international visits and exchanges that will broaden their educational range and provide training in a wide spectrum of materials synthesis and experimental characterization techniques in a collaborative spirit.