Figure 4: Strain engineering of the electronic structures.

(a) Schematic illustration of the two-point bending apparatus using a flexible polyethylene terephthalate (PET) substrate. (b) Schematic illustration of two in-layer hopping parameters ( and ) and one out-of-plane hopping parameter (t^⊥) in a bilayer BP. (c) Extinction spectra (1−T/T₀) of a 6L BP sample under varying tensile strains, with strain applied along the AC (red) and ZZ (blue) directions. The spectra are vertically offset. Here, 0.92%x (0.92%y) indicates applying 0.92% strain along the AC (ZZ) direction. The incident light is polarized along the AC direction. The dashed lines trace the shift in the transition energies. (d) The E₁₁ and E₂₂ peak energies as a function of tensile strains, the strain direction is along the AC (red) and ZZ (blue) directions, respectively. The solid lines are linear fits to the data.