  Controlling the electronic properties via bandstructure engineering is at the
heart of modern semiconductor devices. Here, we extend this concept to
semimetals where, utilizing LuSb as a model system, we show that quantum
confinement lifts carrier compensation and differentially affects the mobility
of the electron and hole-like carriers resulting in a strong modification in
its large, non-saturating magnetoresistance behavior. Bonding mismatch at the
heteroepitaxial interface of a semimetal (LuSb) and a semiconductor (GaSb)
leads to the emergence of a novel, two-dimensional, interfacial hole gas and is
accompanied by a charge transfer across the interface that provides another
avenue to modify the electronic structure and magnetotransport properties in
the ultra-thin limit. Our work lays out a general strategy of utilizing
confined thin film geometries and heteroepitaxial interfaces to engineer
electronic structure in semimetallic systems, which allows control over their
magnetoresistance behavior and simultaneously, provides insights into its
origin.
