On the theory of two-dimensional materials with tilted Dirac cones

倾斜狄拉克锥二维材料理论

• 批准号: 2239575
• 金额: --
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2239575
• 关键词: theory; two; dimensional; materials; tilted

Developing novel materials and metamaterials with "designer" spectra for electrons, photons, magnons and phonons is the growing trend in contemporary condensed matter physics. The tide of research is turning towards theoretical predictions followed by experimental observations of exotic quasiparticles in solid state systems such as Weyl and Majorana fermions. Since the 1980's, two-dimensional (2D) systems provided a particularly rich playground for the discovery of new quasiparticles, including fractionally charged anyons in quantum Hall systems and massless Dirac fermions in graphene and topological insulators as the most spectacular examples. Simultaneously, the most recent advances in nanotechnology include the development of van der Waals heterostructures (artificial few-layer materials held by van der Waals forces) and finding a way of producing carbon nanotubes of selected chirality. The proposed theoretical PhD research will focus on the electronic properties of a novel designer 2D van der Waals material formed by a planar regular array of single-walled carbon nanotubes. Single-walled carbon nanotubes are long cylindrical molecules with electronic properties defined entirely by the way they are rolled from a graphene sheet. Namely, they can be semiconducting with a bandgap up to several electron-volts, metallic without any bandgap or quasi-metallic with a tiny bandgap of a few meV induced by curvature effects. Combining the tubes in a regular planar array should result in a strongly anisotropic dispersion of the emerging 2D quasiparticles. The most interesting results are expected for arrays of metallic and quasi-metallic nanotubes for which the motion normal to the nanotube axis will result in the most dramatic changes in the electronic properties. In particular, a bandgap may be opened in an array of metallic tubes or collapse for quasi-metallic nanotubes. The motion normal to the tube axis will also result in lifting the valley degeneracy in highly-symmetric zigzag nanotubes leading to tilted Dirac cones supporting a new type of 2D Weyl fermions with hyperbolic dispersion. An analytic description of the peculiar low-energy electronic dispersion (dependence of energy on the 2D momentum) in this system will be at the core of the proposed research. We will study a plethora of unique physical effects stemming from this dispersion including unusual magneto-transport phenomena and interband dipole transitions, which are expected to be in the highly sought-after terahertz frequency range.

开发具有电子、光子、磁子和声子“设计”光谱的新型材料和超材料是当代凝聚态物理学的增长趋势。研究潮流正在转向理论预测，随后对固态系统中的奇异准粒子（如外尔费米子和马约拉纳费米子）进行实验观察。自 20 世纪 80 年代以来，二维 (2D) 系统为发现新的准粒子提供了特别丰富的场地，其中最引人注目的例子包括量子霍尔系统中的分数带电任意子以及石墨烯和拓扑绝缘体中的无质量狄拉克费米子。同时，纳米技术的最新进展包括范德华异质结构（由范德华力保持的人造少层材料）的开发以及寻找一种生产具有选定手性的碳纳米管的方法。拟议的理论博士研究将重点关注由单壁碳纳米管平面规则阵列形成的新型设计二维范德华材料的电子特性。单壁碳纳米管是长圆柱形分子，其电子特性完全由它们从石墨烯片卷起的方式决定。也就是说，它们可以是带隙高达几个电子伏特的半导体，没有任何带隙的金属性或具有由曲率效应引起的几兆电子伏的微小带隙的准金属性。将这些管组合成规则的平面阵列应该会导致新兴的二维准粒子产生强烈的各向异性色散。最有趣的结果预计是金属和准金属纳米管阵列，其中垂直于纳米管轴的运动将导致电子特性发生最显着的变化。特别地，带隙可以在金属管阵列中打开，或者对于准金属纳米管而言可以塌陷。垂直于管轴的运动还将导致高度对称锯齿形纳米管中谷简并性的提升，从而导致倾斜的狄拉克锥体支持具有双曲色散的新型二维韦尔费米子。该系统中特有的低能电子色散（能量对二维动量的依赖性）的分析描述将是拟议研究的核心。我们将研究这种色散产生的大量独特的物理效应，包括不寻常的磁输运现象和带间偶极子跃迁，这些效应预计将出现在备受追捧的太赫兹频率范围内。