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

非技术摘要历史上，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。这种前景推动了对新材料和赋予现有材料令人满意的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。随着石墨烯等自由二维(2D)晶体的突破性分离，以及一系列特殊物理性质的发现，材料研究进入了一个新纪元。这些材料的独特特征之一是，由于所有原子都驻留在表面，因此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2D薄膜引入应变，可以对材料和电子性能的形成起到至关重要的作用。这项研究旨在开发策略，以归纳、表征和开发应变作为操纵和工程电子和材料性能的句柄的非凡潜力。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系统地研究新的应变诱导材料的性质成为可能，并释放它们在设备应用中的潜力。研究项目具有强大的教育成分，为各级学生和受训人员提供了极好的机会，以获得使用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(2D)晶体的显著特性之一是可以利用外部应变以受控的方式操纵它们的电子性质。这些材料具有很高的延伸性，具有大的杨氏模数、低的残余应力和极大的断裂强度，这使它们能够承受非常大的应变而不断裂。这项研究旨在开发技术来归纳、表征和开发应变作为操纵和工程电子性能的句柄的非凡潜力。通过拉伸或弯曲2D薄膜来引入应变，可以改变和控制晶格间距和晶体结构，并在形成能带结构和电子动力学方面发挥关键作用。该团队研究了在应变存在的情况下预计会出现的新特性，如打开或关闭光谱带隙、应变诱导的超导电性以及通过控制诱导应变的强度和几何形状来保护拓扑结构的传输特性。用扫描隧道显微镜和朗道能级谱等局域探针以及全球输运测量来表征应变诱导的电子性质。所研究的材料包括石墨烯、过渡金属双卤化物和IV族单醇化合物，其中应变对能带结构和电子动力学的影响预计最为显著。

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.