Atlas of air-stable 2D metals: gapping conditions, alloying rules, and superconductivity

Metals and alloy engineering has enjoyed great design freedom from the immense chemical space spanned by metal elements – about 80% of the periodic table. The same chemical space appears difficult to access for atomically-thin two-dimensional metals, due to their fragility against oxidation. The recent realization of 2D metals intercalating graphene/SiC interfaces suggests a general platform for hosting air-stable 2D metals [1]. We present a first-principles high-throughput survey on the structures and stabilities of all metals in the periodic table that would intercalate a graphene/SiC interface [2]. Trends in the stabilities and structures of these systems follow general rules in metal cohesive energies and metal-Si bonding strengths. A robust bandgap opens for a subset of metals satisfying two conditions: appropriate electron filling and substrate-induced symmetry breaking. I discuss two consequences of this gap opening: alloying rules unique to 2D metals [2] and superconductivity with doped-semiconductor character [1].

[1] N. Briggs et al., Nat. Mater. 19, 637 (2020)
[2] Y. Wang et al., arXiv:2011.01914