Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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 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.

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The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: physics