Progress in Epitaxial Thin‐Film Na₃Bi as a Topological Electronic Material

Abstract

Trisodium bismuthide (Na3Bi) is the first experimentally verified topological Dirac semimetal, and is a 3D analogue of graphene hosting relativistic Dirac fermions. Its unconventional momentum–energy relationship is interesting from a fundamental perspective, yielding exciting physical properties such as chiral charge carriers, the chiral anomaly, and weak anti‐localization. It also shows promise for realizing topological electronic devices such as topological transistors. Herein, an overview of the substantial progress achieved in the last few years on Na3Bi is presented, with a focus on technologically relevant large‐area thin films synthesized via molecular beam epitaxy. Key theoretical aspects underpinning the unique electronic properties of Na3Bi are introduced. Next, the growth process on different substrates is reviewed. Spectroscopic and microscopic features are illustrated, and an analysis of semiclassical and quantum transport phenomena in different doping regimes is provided. The emergent properties arising from confinement in two dimensions, including thickness‐dependent and electric‐field‐driven topological phase transitions, are addressed, with an outlook toward current challenges and expected future progress.

Cataloguing MoSi2N4 and WSi2N4 van der Waals Heterostructures: An Exceptional Material Platform for Excitonic Solar Cell Applications

“…Finally, we note that (Mo,W)Si 2 N 4 /Na 3 Bi are the only Type III vdWHs. Such band alignment arises from the ultralow work function [ 100 ] and the narrow bandgap [ 29 ] nature of Na 3 Bi monolayer (see Figure 2A). The VBM of Na 3 Bi overlaps strongly with the CBM of (Mo,W)Si 2 N 4 , thus leading to the formation of Type III SS contacts.…”

“…[ 28 ] Monolayer MoSi 2 N 4 and WSi 2 N 4 are synthetic 2D semiconductors with exceptional electrical mobilities that outperform the widely studied MoS 2 monolayer, holding great promises in nanoelectronics and sub‐10‐nm transistor applications. [ 29–31 ] Structurally, MoSi 2 N 4 is a septuple‐layered material composed of a transition metal nitride sub‐monolayer (Mo‐N) intercalated between two outer silicon‐nitride (SiN) sub‐monolayers. Such intercalated architecture gives rise to a large family of six‐membered ring monolayers with septuple‐atomic‐layer structure, known as the MA 2 Z 4 monolayer family.…”

Topological phase change transistors based on tellurium Weyl semiconductor

“…In contrast with charge transport mechanism in conventional FETs, the TPCTs can switch between Weyl (chiral anomaly transport, ON state) and conventional semiconductor (charge transport, OFF state), which results in the coexistence of high ON/OFF ratio and high ON-state conductance by shifting the position of E F through electrostatic modulation. The Te TPCTs outperform reported spin/valley/chirality FETs (4, 28, 29), topological insulator-based FETs (30)(31)(32), and Te charge-based FETs (26, 27) (table S1) in terms of both ON-state conductance and ON/OFF ratio, showing great potential for ultralow-power electronics.…”

Large Transverse and Longitudinal Magneto‐Thermoelectric Effect in Polycrystalline Nodal‐Line Semimetal Mg3Bi2

“…The key features of MTE materials with large transverse thermopower have been typically attributed to ultrahigh carrier mobility and electron-hole compensation, which are the exact conditions required for large MR. Owing to the presence of electrons and holes, topological semimetals usually exhibit very high MR, which is even not saturating at higher magnetic field strengths of tens of Tesla. [47,48] Its electrical conductivity σ can be significantly modulated under a magnetic field (Part III, Supporting Information), modifying MR and improving the longitudinal thermopower (Part I, Supporting Information). Therefore, the MR, which reflects the response of the electrical transport properties to a magnetic field, is closely related to the MTE effect.…”