Chapter 5 - Topological properties of MXenes

Abstract

Superconducting materials at room temperature are highly in demand for supercomputing and quantum computing purposes. Topological materials, most often topological insulators (TIs), are also found to conduct like superconductors at their certain regions. In TI, edges and surfaces are conducting, however their bulk is insulating. They are protected with time-reversal symmetry and have effective Spin-Orbit Interaction (SOI). Among several other terminated MXenes, M′xMy″Xene oxide (for x=2 and y=1, 2) has been theoretically found to be stable and has topological insulating property. Our WIEN2k calculation shows more band gap after SOI than the calculation made by M. Khazaei et al. 2015. M′xMy″Xene is a MXene with ordered double transition metals M′ and M″ derived from their parent M′xMy″AXene, where A is an A block element and X is a carbide, nitride, or carbonitride, following the structural composition Mn+1Xn for n=1, 2, or 3. The structure and composition of the parent-phase etched and delaminated ordered double transition metal layered carbide have been studied with the help of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy, and were found to be stable. Oxidation of M′xMy″Xene for experimental verification was another challenge for the selective adsorption of oxygen atoms required on the surface and to preserve bulk under high temperatures. Ablation plasma thrust oxidation adopted in a pulsed laser deposition chamber was successful in such oxidation. The resultant oxide was tested under angle-resolved photoemission spectroscopy (ARPES) and found to be topologically nontrivial. Its electrical, electronic, and magnetic properties are controlled by intercalations and terminations. In this chapter, we are trying to summarize the topologically trivial terminated MXenes and their derivations including our recent research work.