Topological Insulators in Bismuth-Halogen and Related Systems: Design, Synthesis, Optimization and Properties

铋-卤素及相关系统中的拓扑绝缘体：设计、合成、优化和性能

• 批准号: 237598131
• 负责人: Professor Dr. Thomas Doert
• 金额: --
• 依托单位: Professur für Anorganische Chemie II
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/237598131?language=en
• 关键词: Topological; Insulators; Bismuth; Halogen; Related

Employing the concept of "confined metals" in the first funding period, we have established rough guidelines towards the directed search of new topological insulators based on crystal-structure features. A 2D TI fragment embedded as a low-dimensional structural fragment into the bulk structures of bismuth-rich metal-salt hybrids can account for weak or strong 3D TI properties of the entire compound. The salt-like part can be constructed from the highly polar iodide anions that favor for more defect-free, stoichiometric compounds as opposed to chalcogenides. This approach is by now exemplified by two 3D weak topological insulators (Bi14Rh3I9, Bi2TeI) and a 3D strong topological insulator, beta-Bi4I4, which electronic structure is in proximity of both the weak 3D TI phase and the trivial insulator phase. These bulk materials are built by two different 2D TI fragments: a decorated honeycomb intermetallic layer that structurally resembles graphene and a bismuth bilayer, which is a building unit of the elemental bismuth structure. Bi14Rh3I9 is so far the only known 3D weak TI, for which the occurrence of topological edge states was experimentally confirmed. beta-Bi4I4 is the only representative of the strong topological class Z2=1;(1,1,0) and features a highly anisotropic Dirac cone. Our theoretical consideration of the Bi2TeI electronic structure predicts exotic topological surface states beyond the Z2-formalism. Our goal within the second funding period of the Priority Program is to synthesize, explore and functionalize new families of TIs, taking the above mentioned compounds as a starting point. The availability of real materials will promote theoretical and experimental advances for 3D weak TIs that were so far overshadowed by the strong counterparts also due to the lack of specimens. The essential steps in the research program to realize these goals are: 1) Fine-tuning of the available large Bi14Rh3I9 single-crystals for intrinsic electronic and magneto-electronic transport by means of iodine doping, as well as experimental and theoretical assessment of exfoliation, gating and contacting of thin Bi14Rh3I9 layers in order to get access to first simple devices based on a 3D weak TI. 2) Exploration and expansion of a next generation of strong TIs derived from beta-Bi4I4 by synthetic chemistry, DFT-based calculations of electronic structure and topological invariants. 3) Dedicated efforts to push single-crystal growth of Bi2TeI to the highest attainable level in order to investigate the possible co-existence of the weak 3D TI phase and the topological-crystalline-insulator phase that is protected by the mirror crystal symmetry. 4) Identification of new TI candidates with differing structural types via application of the "confined metals"-concept toward the crystal structure and via first-principle electronic structure calculations and direct calculation of topological invariants.

在第一个资助期采用“受限金属”的概念，我们已经建立了基于晶体结构特征的新拓扑绝缘体的定向搜索的粗略指导方针。2D TI片段作为低维结构片段嵌入到富铋金属盐杂化物的体结构中，可以解释整个化合物的弱或强3D TI性质。类似盐的部分可以由高极性的碘离子组成，这种离子有利于形成更无缺陷的化学计量化合物，而不是硫属化合物。目前，该方法已通过两个3D弱拓扑绝缘体（Bi14Rh3I9, Bi2TeI）和一个3D强拓扑绝缘体β - bi4i4得到了验证，其电子结构接近弱3D TI相和普通绝缘体相。这些大块材料是由两种不同的二维TI碎片构成的：一种是装饰的蜂窝状金属间层，其结构类似于石墨烯；另一种是铋双分子层，它是元素铋结构的构建单元。Bi14Rh3I9是迄今为止唯一已知的三维弱钛，其拓扑边缘态的存在已被实验证实。β - bi4i4是强拓扑类Z2=1的唯一代表；（1,1,0），具有高度各向异性的狄拉克锥。我们对Bi2TeI电子结构的理论考虑预测了超越z2形式的奇异拓扑表面态。我们在重点项目第二个资助期内的目标是以上述化合物为起点，合成、探索和功能化新的ti家族。真实材料的可用性将促进3D弱ti的理论和实验进展，迄今为止，由于缺乏样品，强ti的对应物也使其黯然失色。实现这些目标的研究计划的关键步骤是：1)通过碘掺杂对现有的大型Bi14Rh3I9单晶进行本征电子和磁电子输运的微调，以及对薄Bi14Rh3I9层的剥离、门控和接触进行实验和理论评估，以便获得基于3D弱TI的第一个简单器件。2)通过合成化学、基于dft的电子结构和拓扑不变量计算，探索和扩展β - bi4i4衍生的下一代强ti。3)致力于推动Bi2TeI单晶生长到可达到的最高水平，以研究弱3D TI相和受镜像晶体对称性保护的拓扑-晶体-绝缘体相共存的可能性。4)通过对晶体结构的“受限金属”概念的应用，以及通过第一性原理电子结构计算和拓扑不变量的直接计算，确定具有不同结构类型的新TI候选物。