  Strain engineering of graphene takes advantage of one of the most dramatic
responses of Dirac electrons enabling their manipulation via strain-induced
pseudo-magnetic fields. Numerous theoretically proposed devices, such as
resonant cavities and valley filters, as well as novel phenomena, such as snake
states, could potentially be enabled via this effect. These proposals, however,
require strong, spatially oscillating magnetic fields while to date only the
generation and effects of pseudo-gauge fields which vary at a length scale much
larger than the magnetic length have been reported. Here we create a periodic
pseudo-gauge field profile using periodic strain that varies at the length
scale comparable to the magnetic length and study its effects on Dirac
electrons. A periodic strain profile is achieved by pulling on graphene with
extreme (>10%) strain and forming nanoscale ripples, akin to a plastic wrap
pulled taut at its edges. Combining scanning tunneling microscopy and atomistic
calculations, we find that spatially oscillating strain results in a new
quantization different from the familiar Landau quantization observed in
previous studies. We also find that graphene ripples are characterized by large
variations in carbon-carbon bond length, directly impacting the electronic
coupling between atoms, which within a single ripple can be as different as in
two different materials. The result is a single graphene sheet that effectively
acts as an electronic superlattice. Our results thus also establish a novel
approach to synthesize an effective 2D lateral heterostructure - by periodic
modulation of lattice strain.
