  Relativistic Dirac fermions are ubiquitous in condensed matter physics. Their
mass is proportional to the material energy gap and the ability to control and
tune the mass has become an essential tool to engineer quantum phenomena that
mimic high energy particles and provide novel device functionalities. In
topological insulator thin films, new states of matter can be generated by
hybridizing the massless Dirac states that occur at material surfaces. In this
work, we experimentally and theoretically introduce a platform where this
hybridization can be continuously tuned: the Pb1-xSnxSe topological
superlattice. In this system, topological Dirac states occur at the interfaces
between a topological crystalline insulator Pb1-xSnxSe and a trivial insulator,
realized in the form of topological quantum wells (TQW) epitaxially stacked on
top of each other. Using magnetooptical transmission spectroscopy on high
quality MBE grown Pb1-xSnxSe superlattices, we show that the penetration depth
of the TQW interface states and therefore their Dirac mass is continuously
tunable with temperature. This presents a new pathway to engineer the Dirac
mass of topological systems and paves the way towards the realization of
emergent quantum states of matter using Pb1-xSnxSe topological superlattices.
