Electronic Topological Transition of 2D Boron by the Ion Exchange Reaction

We systematically investigated electronic evolutions of nonsymmorphic borophene with chemical environments that were realized by the ion exchange method. Electronic structures can be characterized topological Z2 invariant. Spectroscopic experiments and DFT calculations unveiled a sheet hydrogenated (borophane) is Dirac nodal loop semimetal (Z2=−1), while layered crystal YCrB4 an insulator (Z2=1). The results demonstrate transition replacement counter atoms on layer.