New Method Creates Moiré 2D Materials Using Strain, Not Twisting

Researchers have developed a new method to create moiré patterns in two-dimensional (2D) materials. This technique uses controlled strain rather than the traditional twisting and stacking of material layers. Moiré patterns are atomic-scale structures that can give materials unique quantum properties.

Since 2018, scientists have shown that slightly twisted graphene layers can exhibit superconductivity. Moiré patterns form when ultra-thin material layers are stacked with a slight misalignment. This misalignment changes the atomic lattices, affecting how electrons move through the material. These changes can lead to quantum behaviors like correlated insulating states, magnetism, and superconductivity.

Previous methods for engineering moiré patterns involved manually rotating and stacking 2D material flakes. This process is difficult to reproduce and scale up for larger applications. The new approach uses thin-film coatings to apply controlled strain to layers of molybdenum disulfide. This generates moiré superlattices across the material.

This strain-based method offers a predictable and scalable way to create quantum materials. It uses common fabrication techniques. Strain engineering is already a standard practice in semiconductor manufacturing. Companies use techniques like silicon-germanium alloys and stressed metal coatings to strain silicon and improve transistor performance. The inspiration for this new method came from observations that metal stressor films could strain 2D materials.

The researchers deposited lithographically patterned stressor films onto molybdenum disulfide flakes. These films locally pulled and compressed the upper atomic layers. This created different strain environments across the material. Near the edges of the patterned films, the strain was primarily biaxial. Regions farther away experienced mostly uniaxial strain. This produced different moiré geometries and localized electric polarization in the molybdenum disulfide, which is typically nonpolar.

The researchers are now investigating how these polar domains can be integrated into functional electronic devices. The polarization could potentially be switched with an electric field. This effect might be used to tune electrical resistance at the nanoscale. The new method could make moiré physics research more accessible to a wider range of scientists.