Spatial charge inhomogeneity and defect states in topological Dirac semimetal thin films of Na ₃ Bi

Abstract

Small potential variations in 3D semimetal Na3Bi enable close approach to the Dirac point, allowing exploration of new physics.

Dimensional Crossover and Topological Phase Transition in Dirac Semimetal Na3Bi Films

“…The dip becomes less clear with increasing thickness and completely disappear for thick films, gradually evolving into the bulk limit ( Figure S5). 30 These spectroscopic characteristics reveal that the DSM Na3Bi experiences a smooth 3D-to-2D dimensional crossover with gap-opening in reduced dimension, from a bulk gapless DSM to a gapped insulator. Similar phenomena of Dirac gap-opening by varying film thickness have been reported for 3D TI Bi2Se3 films.…”

Importance of interactions for the band structure of the topological Dirac semimetal Na3Bi

“…Topological Dirac semi-metals (TDS) such as Na 3 Bi and Cd 3 As 2 are a new class of materials featuring two degenerate Weyl points with opposite topological charge occurring at the same momentum protected by time reversal symmetry and rotation and inversion. [1][2][3][4] TDS materials have yielded exciting physical properties, such as ultra-low potential fluctuations comparable to the highest quality graphene on h-BN, 5 the chiral anomaly, 6,7 Shubnikov de-Haas oscillations consistent with Weyl orbits, 8 weak anti-localization with phase coherence lengths of up to 1 µm, 9 Dirac gap dependence on the film thickness, 10 and an electric field induced transition from topological insulator to conventional insulator in ultra-thin Na 3 Bi. 11 The low-energy bandstructure of Na 3 Bi results from the overlap of the conduction band dominated by Na-3s states and the valence band dominated by Bi-6p states.…”

Temperature-dependent n−p transition in a three-dimensional Dirac semimetal Na3Bi thin film

“…Due to better electronic screening in 3D, spatial fluctuations in Fermi energy in 3D TDS are expected to be much smaller for a comparable disorder. Indeed, low fluctuations in E F of 4 ∼ 6 meV = 40 ∼ 70 K were observed in thin film Na 3 Bi, suggesting the regime T ≥ T F is experimentally accessible [8].…”

“…Na 3 Bi is a topological Dirac semimetal (TDS) with stable 3D Dirac points separated form the Γ point along the k z axis in its 1st Brillouin zone which has a linear band dispersion in all three momentum space directions [3,4]. The behavior of Dirac fermions in 3D opens up the possibility to study phenomena such as the chiral anomaly [5,6]; thin films geometry offers the opportunity to study ambipolar electronic devices [7], electron-hole pudding [8], along with the theoretical prediction of opening a band gap in excess of 300 meV in monolayer films [9] and a topological phase transition between trivial and non-trivial insulator that occurs at varying thickness or with applied electric field [10,11].…”