  We demonstrate that stacking layered materials allows a novel type of strain
engineering where each layer is strained independently, which we call
heterostrain. We combine detailed structural and spectroscopic measurements
with tight-binding calculations to show that small uniaxial heterostrain
suppresses Dirac cones and leads to the emergence of flat bands in twisted
graphene layers (TGLs). Moreover, we demonstrate that heterostrain reconstructs
much more severely the energy spectrum of TGLs than homostrain for which both
layers are strained identically ; a result which should apply to virtually all
van der Waals structure opening exciting possibilities for straintronics with
2D materials.
