  Heusler compounds, in both cubic and hexagonal polymorphs, exhibit a
remarkable range of electronic, magnetic, elastic, and topological properties,
rivaling that of the transition metal oxides. To date, research on these
quantum materials has focused primarily on bulk magnetic and thermoelectric
properties or on applications in spintronics. More broadly, however, Heuslers
provide a platform for discovery and manipulation of emergent properties at
well-defined crystalline interfaces. Here, motivated by advances in the
epitaxial growth of layered Heusler heterostructures, I present a vision for
Heusler interfaces, focusing on the frontiers and challenges that lie beyond
spintronics. The ability to grow these materials epitaxially on technologically
important semiconductor substrates, such as GaAs, Ge, and Si, provides a direct
path for their integration with modern electronics. Further advances will
require new methods to control the stoichiometry and defects to "electronic
grade" quality, and to control the interface abruptness and ordering at the
atomic scale.
