Strain Engineering of Band Structure and Electronic Properties in Two Dimensional Materials.

从历史上看，新材料特性的发现一直是技术进步、繁荣和社会福祉的引擎。这一前景推动了对新材料和技术的长期探索，以赋予现有材料理想的性能。传统上，材料的发现是对无数化学合成化合物进行艰苦探索的结果。随着独立二维（2D）晶体（如石墨烯）的分离取得突破性进展，以及它们一系列特殊物理性质的发现，材料研究进入了一个新时代。这些材料的一个独特的特点是，所有的原子都在表面，可以通过非化学手段获得和操纵它们的性质。特别是通过拉伸或弯曲二维薄膜而引入的应变，可以在塑造材料和电子性能方面发挥关键作用。本研究旨在开发策略，以诱导，表征和利用应变作为操纵和工程电子和材料特性的处理的非凡潜力。通过改变原子之间的距离和晶体结构的几何形状，应变可以改变材料的性质，并有可能从根本上改变其行为。在受控物质中引入应变的方法的发展将使系统地研究新的应变诱导材料特性并释放其在器件应用中的潜力成为可能。该研究项目具有很强的教育成分，为各级学生和学员提供了极好的机会，以获得先进科学设备的实践经验，并发展复杂的数据分析技能。技术摘要二维晶体的显著特性之一是可以利用外部应变以可控的方式操纵其电子特性。这些材料具有高度可拉伸性，具有大的杨氏模量，低残余应力和巨大的断裂强度，使它们能够承受非常大的应变而不断裂。本研究旨在开发技术，以诱导，表征和利用应变作为操纵和工程电子特性的处理的非凡潜力。通过拉伸或弯曲二维薄膜来引入应变，使得改变和控制晶格间距和晶体结构成为可能，并且在形成能带结构和电子动力学方面起着至关重要的作用。该团队研究了在应变存在下可能出现的新特性，例如打开或关闭光谱间隙、应变诱导超导性以及通过控制诱导应变的强度和几何形状来实现拓扑保护传输特性。局部探针，如扫描隧道显微镜和朗道能级光谱以及全局输运测量被用来表征应变诱导的电子性质。研究的材料包括石墨烯、过渡金属二硫族化合物和IV族单硫族化合物，其中应变对能带结构和电子动力学的影响最为明显。

Nontechnical abstractThe discovery of new material properties has historically been an engine for technological advances, prosperity and societal well-being. This prospect has fueled an age-old search for new materials and for techniques to endow existing ones with desirable properties. Traditionally, materials discovery was the result of painstaking exploration of a myriads of chemically synthesized compounds. A new era of materials research was ushered in with the breakthrough isolation of free standing two-dimensional (2D) crystals, such as graphene, and the discovery of a slew of their exceptional physical properties. One of the unique characteristics of these materials is that, with all the atoms residing at the surface, it is possible to access and manipulate their properties by non-chemical means. In particular the introduction of strain by stretching or bending the 2D membrane, can play a crucial role in shaping the material and electronic properties. This research is aimed at developing strategies to induce, to characterize and to exploit the extraordinary potential of strain as a handle for manipulating and engineering electronic and material properties. By modifying the distance between atoms and the geometry of the crystal structure, strain can transform the material properties and has the potential to radically change its behavior. The development of methods to introduce strain in a controlled matter will make it possible to systematically investigate novel strain-induced material properties and unleash their potential for device applications. The research project has a strong educational component that provides excellent opportunities for students and trainees at all levels to gain hands-on experience with advanced scientific equipment and to develop sophisticated data analysis skills. Technical abstractOne of the remarkable qualities of two-dimensional (2D) crystals is the possibility to use external strain to manipulate in a controlled manner their electronic properties. These materials are highly stretchable, have large Young's modulus, low residual stress and enormously large breaking strength which enables them to sustain very large strains without breaking. This research aims at developing techniques to induce, characterize and exploit the extraordinary potential of strain as a handle for manipulating and engineering electronic properties. Introduction of strain by stretching or bending a 2D membrane, makes it possible to change and control the lattice spacing and crystal structure and can play a crucial role in shaping the band structure and the electron dynamics. The team investigates novel properties expected to arise in the presence of strain, such as opening or closing spectral gaps, strain induced superconductivity and topologically protected transport properties by controlling the strength and geometry of the induced strain. Local probes such as scanning tunneling microscopy and Landau level spectroscopy as well as global transport measurements are used to characterize the strain-induced electronic properties. The materials studied include graphene, transition metal dichalcogenides and group IV monochalcogenides, where the effects of strain on the band structure and electron dynamics are expected to be most pronounced.