Dirac parameters and topological phase diagram of Pb1-xSnxSe from magnetospectroscopy

Pb1-xSnxSe hosts three-dimensional (3D) massive Dirac fermions across the entire composition range for which the crystal structure is cubic. In this paper, we present a comprehensive experimental mapping of the 3D band structure parameters of Pb1-xSnxSe as a function of composition and temperature. We cover a parameter space spanning the band inversion that yields its topological crystalline insulator phase. A nonclosure of the energy gap is evidenced in the vicinity of this phase transition. Using magneto-optical Landau level spectroscopy, we determine the energy gap, Dirac velocity, anisotropy factor, and topological character of Pb1-xSnxSe epilayers grown by molecular beam epitaxy on BaF2 (111). Our results are evidence that Pb1-xSnxSe is a model system to study topological phases and the nature of the phase transition.