Topological Dirac Semimetal Na3Bi Films in the Ultrathin Limit via Alternating Layer Molecular Beam Epitaxy

TL;DR

This paper reports the successful fabrication of uniform, ultrathin Na3Bi films using alternating layer molecular beam epitaxy, enabling exploration of quantum effects in topological Dirac semimetals.

Contribution

It introduces a novel MBE growth method for continuous, high-quality ultrathin Na3Bi films on insulating substrates, advancing the study of quantum phenomena in these materials.

Findings

Achieved 3.8 nm thick Na3Bi films with high crystallinity.

Confirmed film quality through multiple characterization techniques.

Demonstrated atomic layer-by-layer growth using seed layers.

Abstract

Ultrathin films of Na3Bi on insulating substrates are desired for opening a bulk band gap and generating the quantum spin Hall effect from a topological Dirac semimetal, though continuous films in the few nanometer regime have been difficult to realize. Here, we utilize alternating layer molecular beam epitaxy (MBE) to achieve uniform and continuous single crystal films of Na3Bi(0001) on insulating Al2O3(0001) substrates and demonstrate electrical transport on films with 3.8 nm thickness (4 unit cells). The high material quality is confirmed through in situ reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). In addition, these films are employed as seed layers for subsequent growth by codeposition, leading to atomic layer-by-layer growth as indicated by RHEED intensity oscillations. These material advances facilitate the pursuit of quantum phenomena in thin films of Dirac semimetals.