Strain-Modulated Emergence of Rectangular Moiré Superlattice in Transition Metal Dichalcogenide van der Waals Heterostructures*

The existence of moiré superlattice in van der Waals heterostructures brings highly tunable electronic structure , which enables the moiré heterostructures to simulate quantum phenomena in condensed-matter systems. Currently, the size and symmetry of moiré superlattice are controlled by monolayer material choice and twist angle between layers. However, they are inferior to continuous tuning after heterostructure fabrication. Here we show that strain application is suitable for continuous size and symmetry control of the superlattice. We fabricated twisted bilayer WSe₂ on flexible substrate. By bending the substrate, uniaxial strain was intentionally applied to the sample. Based on the theoretical model, we were able to design the expected moiré superlattice under combined twist angle and strain condition. We then successfully observed the continuous distortion of moiré superlattice from triangular to rectangular. Corresponding band structure calculation indicatess strong anisotropy and tunable flat-band property in strained sample. The established method and observation pave the way for utilizing strain a new tuning parameter to modulate the correlated behavior in moiré superlattices.