Tunable Dirac interface states in topological superlattices

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 paper, 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 (TQWs) epitaxially stacked on top of each other. Using magnetooptical transmission spectroscopy on high-quality molecular-beam epitaxy grown Pb1−xSnxSe superlattices, we show that the penetration depth of the TQW interface states and therefore their Dirac mass are continuously tunable with temperature. This presents a 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.