At Cornell University's Duffield College of Engineering, researchers have cracked a problem that has limited quantum materials science for years: how to reliably manufacture the strange, useful structures called moiré patterns without painstaking manual labor. Their solution uses a technique semiconductor companies have relied on for decades—controlled strain applied through patterned thin films—to engineer moiré superlattices in molybdenum disulfide, a discovery published in the Proceedings of the National Academy of Sciences.
Since 2018, when scientists discovered that slightly twisted graphene layers could exhibit superconductivity, moiré materials have captivated researchers. These atomic-scale structures form when ultra-thin material layers are stacked slightly out of alignment, creating subtle shifts in the atomic lattice that fundamentally change how electrons move through the material. The result can be exotic quantum behaviors: correlated insulating states, magnetism, and superconductivity. But making these materials has required painstaking manual manipulation—twisting and stacking individual 2D flakes by hand, a process with poor reproducibility and almost no path to large-scale manufacturing.
Judy Cha, the Rick and Betty Tsai Professor in Materials Science and Engineering, led the team that developed an alternative. Rather than physically stacking materials, they deposit lithographically patterned stressor films directly onto molybdenum disulfide flakes. These films locally pull and compress the upper atomic layers, creating different strain environments across a single piece of material. Near the edges of the patterned films, the strain is primarily biaxial—pulling in two directions simultaneously—while regions farther away experience mostly uniaxial strain, producing entirely different moiré geometries from a single fabrication step.
The real elegance lies in the simplicity. "Strain engineering is already a standard part of semiconductor manufacturing," Cha explained. "For decades, companies have used approaches like silicon-germanium alloys and stressed metal coatings to deliberately strain silicon and boost transistor performance." The inspiration came when Cha realized that if metal stressor films could strain 2D materials, the different strain layers might generate moiré patterns because upper atomic layers would deform differently from those beneath them. The prediction held.
What emerges is both surprising and useful: the different strain environments generate localized electric polarization in molybdenum disulfide, a material that is normally nonpolar. Along boundaries between moiré domains, tiny shifts in atomic registry create in-plane polarization textures whose orientation depends on the underlying strain geometry. Because this polarization can potentially be switched with an electric field, researchers see a path toward tuning electrical resistance at the nanoscale—a property with clear device applications.
Perhaps most importantly, this approach opens moiré physics to researchers who lack extensive stacking expertise. "This is a very standard lithography step and everybody who makes devices does this every day," Cha said. "I hope that this opens the door so that people who have not really done extensive stacking to make moiré potentials can explore this approach." By lowering the barrier to entry, the discovery could accelerate investigation into quantum phenomena and accelerate the path from laboratory discovery to practical devices. The researchers are now exploring whether the polar domains can be incorporated into functioning electronic devices, a natural next step that could make quantum materials engineering as routine as any other silicon-based manufacturing process.