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

TL;DR

This study demonstrates the successful fabrication and characterization of pure, stable, strained $eta$-Sn films exhibiting 3D topological Dirac semimetal states, confirmed through advanced spectroscopic techniques.

Contribution

It introduces a reliable method to grow pure strained $eta$-Sn films without doping or substrate heating, enabling exploration of topological properties.

Findings

Detection of compressive strain via Mössbauer spectroscopy

Confirmation of topological Dirac cone through ARPES

Enhanced understanding of electronic structure above Fermi level

Abstract

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 of 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 M\"ossbauer 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 obtaining an improved insight into the electronic structure of the 3D topological Dirac semimetal $\alpha$-Sn above the Fermi level.