Twist and Strain in Square Moiré Patterns of Stacked Graphene Layers.

We report the first observation of controlled, strain-induced square moiré patterns in stacked graphene. By selectively displacing native wrinkles, we drive a reversible transition from the usual trigonal to square moiré order. Scanning tunneling microscopy reveals elliptically shaped AA domains, while spectroscopy shows strong electronic correlation in the form of narrow bands with split Van Hove singularities near the Fermi level. A continuum model with electrostatic interactions reproduces these features under the specific twist-strain combination that minimizes elastic energy. This Letter demonstrates that the combination of twist and strain, or twistraintronics, enables the realization of highly correlated electronic states in moiré heterostructures with geometries that were previously inaccessible.