Continuous Strain Modulation of Moiré Superlattice Symmetry From Triangle to Rectangle

Moiré superlattices formed in van der Waals (vdW) bilayers of 2D materials provide an ideal platform for studying previously undescribed physics, including correlated electronic states and moiré excitons, owing to the wide-range tunability of their lattice constants. However, their crystal symmetry is fixed by the monolayer structure, and the lack of a straightforward technique for modulating the symmetry of moiré superlattices has impeded progress in this field. Herein, a simple, room-temperature, ambient method for controlling superlattice symmetry is reported. The method uses vdW heterostructures on a flexible substrate; by bending the substrate, a uniaxial strain is introduced. Based on numerical calculations, a strain condition is designed to deform the moiré superlattice from triangular to rectangular, and visualized the continuous deformation of real-space moiré superlattices using piezoresponse force microscopy. The band calculations show that nearly flat moiré minibands remain in the rectangular lattice; therefore, this method provides an additional tuning knob for the Hamiltonian of moiré quantum matter.