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

Abstract

In-plane compressively strained α-Sn films have been theoretically predicted and experimentally proven to possess nontrivial 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.

Switching of a Magnet by Spin‐Orbit Torque from a Topological Dirac Semimetal

“…It is noteworthy that the surface morphology of the α‐Sn film is very similar to that of α‐Sn films grown previously by molecular beam epitaxy (MBE). [ 29 ] Figure 2c indicates an α‐Sn grain size in the 15–20 nm range, which is comparable to the range of grain sizes for MBE‐grown films. [ 29 ]…”

“…[ 29 ] Figure 2c indicates an α‐Sn grain size in the 15–20 nm range, which is comparable to the range of grain sizes for MBE‐grown films. [ 29 ]…”

“…This is plausible, in that the α‐Sn film consists of nanoscale grains {see Figure 2c and Ref. [ 29 ] }. (3) Finally, the presence of the TSS in sputtered α‐Sn thin films has been recently confirmed from a comprehensive ferromagnetic resonance study on a series of Sn/ferromagnet layered structures.…”

Large Damping Enhancement in Dirac‐Semimetal–Ferromagnetic‐Metal Layered Structures Caused by Topological Surface States

“…This is consistent with the expectation—the α‐Sn film grown on the InSb substrate should exhibit an in‐plane compressive strain because the lattice constant of α‐Sn is slightly larger than that of InSb. [ 15,20,21 ] The Voigt fitting yields a = 6.489 ± 0.005 Å for the α‐Sn film, which corresponds to a tensile strain of (0.27 ± 0.08)%. Such a strain makes the α‐Sn film a TDS.…”

“…The lattice constant of α‐Sn ( a = 6.489 Å) is slightly larger than that of InSb ( a = 6.479 Å), and this lattice mismatching gives rise to an in‐plane compressive strain or a perpendicular tensile strain in the α‐Sn films. [ 15,20,21 ] The work made use of layered α‐Sn(6 nm)/Ag(2 nm)/NiFe(20 nm) structures where the NiFe film is ferromagnetic, and the nonmagnetic Ag layer works as a spacer to physically separate α‐Sn and NiFe and thereby avoid the suppression of TSS in α‐Sn by the magnetic ordering in the NiFe film. The damping in these structures is found to be a factor of about 4.8 bigger than in the single‐layer NiFe film.…”