Niels Claessens | Searcharxiv

arXiv2021

Non-trivial quantum magnetotransport oscillations in pure and robust topological $α$-Sn films

We report experimental evidence of topological Dirac fermion charge carriers in pure and robust $α$-Sn films grown on InSb substrates. This evidence was acquired using standard macroscopic four-point contact resistance measurements, conducted on uncapped films with a significantly reduced bulk mobility. We analyzed and compared electrical characteristics of the constituting components of the $α$-Sn/InSb sample, and propose a three-band drift velocity model accordingly. A surface band, with low carrier density and high mobility, is identified as the origin of the observed Shubnikov -- de Haas oscillations. The analysis of these quantum oscillations results in a non-trivial value of the phase shift $γ=0$, characteristic for topologically protected Dirac fermions. For the same uncapped samples we estimate the momentum relaxation time $τ\approx 300\ \mathrm{fs}$, which is significantly larger in comparison with the previous reports on grown $α$-Sn films.

cond-mat.mtrl-sci↗

arXiv2020

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

In-plane compressively strained $α$-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 $α$-Sn films on InSb(100), without heating of the substrate during growth, nor using any dopants. The $α$-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 Mössbauer 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 $α$-Sn above the Fermi level.

cond-mat.mtrl-sci↗