Experimental evidence of monolayer AlB2 with symmetry-protected Dirac cones

Monolayer AlB2 is composed of two atomic layers: honeycomb borophene and triangular aluminum. In contrast with the bulk phase, monolayer AlB2 is predicted to be a superconductor with a high critical temperature. Here, we demonstrate that monolayer AlB2 can be synthesized on Al(111) via molecular beam epitaxy. Our theoretical calculations revealed that the monolayer AlB2 hosts several Dirac cones along the Γ-M and Γ-K directions; these Dirac cones are protected by crystal symmetries and are thus resistant to external perturbations. The extraordinary electronic structure of the monolayer AlB2 was confirmed via angle-resolved photoemission spectroscopy measurements. These results are likely to stimulate further research interest to explore the exotic properties arising from the interplay of Dirac fermions and superconductivity in two-dimensional materials.