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

非技术摘要新材料特性的发现历来是技术进步、繁荣和社会福祉的引擎。这一前景推动了对新材料和赋予现有材料所需性能的技术的长期探索。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。随着石墨烯等独立二维（2D）晶体的突破性分离以及一系列特殊物理特性的发现，迎来了材料研究的新时代。这些材料的独特特性之一是，由于所有原子都位于表面，因此可以通过非化学手段访问和操纵它们的特性。特别是通过拉伸或弯曲2D膜来引入应变，可以在材料和电子特性的成形中发挥至关重要的作用。这项研究的目的是制定战略，以诱导，表征和利用应变作为操纵和工程电子和材料性能的手柄的非凡潜力。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得有可能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。该研究项目有一个强大的教育组成部分，为各级学生和受训人员提供了极好的机会，以获得先进科学设备的实践经验，并培养复杂的数据分析技能。二维（2D）晶体的显著特性之一是可以使用外部应变以受控方式操纵其电子性质。这些材料是高度可拉伸的，具有大的杨氏模量、低的残余应力和极大的断裂强度，这使得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手柄的非凡潜力。通过拉伸或弯曲2D膜来引入应变，使得可以改变和控制晶格间距和晶体结构，并且可以在形成能带结构和电子动力学方面发挥至关重要的作用。该团队研究了在应变存在下预计会出现的新特性，例如打开或关闭光谱间隙，应变诱导的超导性和通过控制诱导应变的强度和几何形状来拓扑保护的传输特性。局部探针，如扫描隧道显微镜和朗道能级光谱以及全球运输测量用于表征应变诱导的电子性质。研究的材料包括石墨烯，过渡金属二硫属化物和IV族单硫属化物，其中应变对能带结构和电子动力学的影响预计是最明显的。

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.