Bursting at the Seams: Rippled Monolayer Bismuth on NbSe2

One of the heaviest semimetals in nature, bismuth ignited the interest of the materials-physics community for its potential impact on topological quantummaterial systems that utilize its strong spin-orbit coupling (SOC) and unique orbital hybridization. In particular, recent theoretical predictions of unique topological and superconducting properties of thin bismuth films and interfaces prompted intense research on the growth of sub- to a few monolayers of bismuth on different substrates. Similar to bulk rhombohedral bismuth, the initial growth of bismuth films on most substrates results in buckled hexagonal bilayers that either grow in the (111) or (110) directions, with a lattice constant close to that of the bulk. By contrast, in this paper we show a new unpredicted growth paradigm for bismuth monolayers. Using a freshly cleaved NbSe2 as a substrate, we show that the initial growth of Bi can strongly bond, 1 while conforming to the lattice constant of the top Se-layer of NbSe2, resulting in a compressed two-dimensional triangular lattice. The enormous strain is relieved during growth by developing a unique pattern of ripples and local strain, which also introduces strong marks on the electronic properties at the surface.