Strain engineering of 2D materials

The strain engineering is a powerful paradigm for modifying the band structure of 2D materials, and hence enabling their electrical and optical properties to be beautifully engineered. However, it still remains a challenge to arbitrarily control the magnitude and distribution of the strain, limiting the extent to which the strain engineering of 2D materials can effectively operate and advance in both fundamental studies and technological applications. In this talk, I will present a method that we developed to strain engineer the 2D materials by conforming it onto the hexagonal boron nitride (hBN) with lithographically-patterned surface nanostructures. We then demonstrate the arbitrary control of the strain and hence the electronic band structure of MoS2 through Raman spectroscopy and photoluminescence. We have also used this approach to realize an unusual electronic state in a corrugated bilayer graphene system in which strain and interlayer interactions are specially engineered to induce pseudo-magnetic fields and break the spatial inversion symmetry. This induces a Rashba-like valley–orbit coupling and creates tilted mini-Dirac cones with non-trivial and anisotropic energy dispersion as well as the momentum-space Berry curvature dipole, thereby giving rise to the nonlinear anomalous Hall effect and a new type of planar Hall effect, namely, the pseudo- planar Hall effect without breaking the time reversal symmetry. The capability to artificially create nontrivial band structure and Berry curvature dipoles from conventional two-dimensional materials such as graphene via lithographically-patterned lattice deformation may open a new door to explore study novel geometrical and/or topological quantum phenomena.