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

Nontechnical abstract

The 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 abstract

One 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.