  Using scanning tunneling spectroscopy we have measured the response of Dirac
electrons in a magnetic field to the presence of a well-defined smoothly
varying 1D periodic potential. We find that the lower index Landau level
energies reliably trace the potential variations, while the higher index levels
appear surprisingly homogeneous. Modeling the effects of the periodic potential
on the Landau level spectra, we show that the Landau level behavior encodes
information on the spatial extent of the wavefunctions. The lower index maps
reveal Landau level stripes, which would act as traps for chiral
one-dimensional modes. Our findings have important implications for transport
and magneto-resistance measurements in Dirac materials with engineered
potential landscapes.
