APL Materials (Aug 2018)
Topological Dirac semimetal Na3Bi films in the ultrathin limit via alternating layer molecular beam epitaxy
Abstract
Ultrathin films of Na3Bi on insulating substrates are desired for opening a bulk bandgap 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 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 reflection high-energy electron diffraction, scanning tunneling microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy.