Realization of elemental topological Dirac semimetal α-Sn with high quantum mobility*

α-Sn, the only elemental material that shows multiple topological phases, is promising for topological physics and devices [1]. Here, we have successfully grown α-Sn thin films with the highest quality thus far on InSb(001) substrates by molecular beam epitaxy. Transmission electron microscopy lattice images confirm a diamond-type crystal structure of a-Sn and a perfectly flat interface with an InSb buffer layer. The conductance exhibits strong Shubnikov-de Haas (SdH) oscillations, which are observed at a magnetic field as small as 0.3 T at 2 K and persist up to 20 K, manifesting the high sample quality. From the SdH oscillations, we estimate unprecedentedly high quantum mobilities of both the topological surface states (TSS, 30000 cm²/Vs), which is ten times higher than the previously reported values [2], and the bulk heavy-hole (HH) state (1800 cm²/Vs). Both the TSS and HH bands have nontrivial phase shift, indicating that our α-Sn samples are in a topological Dirac semimetal (TDS) phase. Furthermore, we demonstrate a crossover from TDS to a two-dimensional topological insulator and a subsequent phase transition to a trivial insulator when varying the thickness of α-Sn [3].

[1] D. Zhang, et al., Phys. Rev. B 97, 195139 (2018).[2] Q. Barbedienne et al., Phys. Rev. B 98, 195445 (2018). [3] L. D. Anh et al., Adv. Mater, 2104645 (2021).