Topological State Observations in the Dirac Semimetal Bi₄Se₃ by C-AFM

Bi₄Se₃ is a topological semimetal with spintronics, magnetometers, and optical sensor applications. Bi₄Se₃ is an intrinsic superlattice comprised of a 2D Bi₂ sheet and a quintuple layer (QL) slab of Bi₂Se₃. The 2D Bi₂ sheet supports a Dirac cone at the Fermi level, whereas the QL slab hosts a topologically protected state within the valence band. These films were grown using a custom-built ultra-high vacuum (UHV) sputtering epitaxy system. We grew a sparsely populated hexagonal and trigonal prism crystal form within a background of 001-oriented layers, enabling an isolated study of these layers. We characterized the morphology and local transport properties via conductive atomic force microscopy (C-AFM) with a platinum-coated silicon probe. We observed edge states on the terrace edges of the 001 layers. We observe these as a function of applied force and compare experimental IV-spectroscopy curves to several possible theoretical transport models. At the lowest applied forces on a Bi₂ termination, we observe a Dirac cone in the dI/dV spectroscopy, which agrees with our previous scanning tunneling spectroscopy measurements.