2D Mg-Cu Intermetallic Compounds with Nontrivial Band Topology and Dirac Nodal Lines

Synthesis of vertical heterostructures that include atomically thin layers of materials with topologically nontrivial energy bands is desirable for exploring exotic quantum states. Here, the authors report on atomic-layer-by-layer deposition of magnesium on copper(111) surface by molecular beam epitaxy, monitored in situ by low-energy electron microscopy and diffraction, and modeled by ab initio theory. It is found that a 2D MgCu₂ intermetallic compound forms during initial Mg deposition and persists till a full monolayer of Mg is formed. Deposition of additional Mg triggers a phase transition from the commensurate MgCu₂ to an incommensurate Mg₂Cu layer and enables growth of the second layer of Mg. Ab initio calculations indicate non-trivial topology of the electron bands in the interfacial Mg₂Cu layer and the existence of Dirac nodal lines near the Fermi level. The new 2D Mg₂Cu material emerges as a promising platform to study new topological states of matter.