Towards topological electronics: Epitaxial thin films of topological Dirac semimetal Na3Bi

I will discuss our experiments on epitaxial thin films of topological Dirac semimetal Na₃Bi as a route to novel topological electronic phenomena and devices, including the conventional-to-topological quantum phase transition (QPT) as a function of layer thickness and a topological transistor based on an electric field-tuned QPT. Na₃Bi thin films are grown by molecular beam epitaxial and transferred in UHV to a low-temperature STM capable of magnetotransport at 5 K. Thin films (20 nm) of Na₃Bi on α-Al₂O₃(0001) substrates have low temperature charge carrier mobilities exceeding 6000 cm²V^-1s^-1 with n-type carrier densities below 1 x 10¹⁸ cm^-3[1], comparable to single crystal values. Mapping the local Dirac point via scanning tunneling spectroscopy reveals a high degree of spatial uniformity, with rms variations in Dirac point energy less than 5 meV[2], comparable to the best graphene samples on hexagonal boron nitride. Chemical doping[3] and electrostatic gating[4] (using SiO₂/Si substrates) can be used to tune the carrier density, first steps toward a topological transistor.

[1] J. Hellerstedt et al., Nano Letters 16, 3210 (2016).
[2] M.T. Edmonds et al., ArXiv:1612.03385.
[3] M.T. Edmonds et al., ACS Appl. Mater. Interfaces 8, 16412 (2016).
[4] J. Hellerstedt et al., arXiv:1707.09286.