Structural and electronic properties of the pure and stable elemental 3D topological Dirac semimetal alpha-Sn

In-plane compressively strained alpha-Sn films have been theoretically predicted and experimentally proven to possess non-trivial electronic states of a 3D topological Dirac semimetal. The robustness of these states typically strongly depends on purity, homogeneity, and stability of the grown material itself. By developing a reliable fabrication process, we were able to grow pure strained alpha-Sn films on InSb(100), without heating the substrate during growth nor using any dopants. The alpha-Sn films were grown by molecular beam epitaxy, followed by experimental verification of the achieved chemical purity and structural properties of the film's surface. Local insight into the surface morphology was provided by scanning tunneling microscopy. We detected the existence of compressive strain using Mossbauer spectroscopy, and we observed a remarkable robustness of the grown samples against ambient conditions. The topological character of the samples was confirmed by angle-resolved photoemission spectroscopy, revealing the Dirac cone of the topological surface state. Scanning tunneling spectroscopy, moreover, allowed us to obtain an improved insight into the electronic structure of the 3D topological Dirac semimetal alpha-Sn above the Fermi level.