  In nearly free electron theory the imposition of a periodic electrostatic
potential on free electrons creates the bandstructure of a material, determined
by the crystal lattice spacing and geometry. Imposing an artificially designed
potential to the electrons confined in a GaAs quantum well makes it possible to
engineer synthetic two-dimensional band structures, with electronic properties
different from those in the host semiconductor. Here we report the fabrication
and study of a tuneable triangular artificial lattice on a GaAs/AlGaAs
heterostructure where it is possible to transform from the original GaAs
bandstructure and Fermi surface to a new bandstructure with multiple artificial
Fermi surfaces simply by altering a gate bias. For weak electrostatic potential
modulation magnetotransport measurements reveal quantum oscillations from the
GaAs two-dimensional Fermi surface, and classical oscillations due to these
electrons scattering from the artificial lattice. Increasing the strength of
the modulation reveals new quantum oscillations due to the formation of
multiple artificial Fermi surfaces, and ultimately to new classical
oscillations of the electrons from the artificial Fermi surface scattering from
the superlattice modulation. These results show that low disorder gate-tuneable
lateral superlattices can be used to form artificial two dimensional crystals
with designer electronic properties.
