Emergence of electric polarity in BiTeX (X = Br and I) monolayers and the giant Rashba spin splitting.

A number of graphene-like materials have been theoretically predicted and experimentally confirmed so far. Here, based on the first-principles calculations, we predict that stable BiTeX (X = Br and I) monolayers possess intrinsic large polar electric fields along the normal direction to the plane, making them two-dimensional polar systems. Moreover, we find that these novel monolayers with thicknesses of only 3.8 Å can produce a giant Rashba spin splitting derived from their peculiarly polar atomic configurations. Furthermore, the Rashba parameters of BiTeX monolayers can be effectively modulated by applying strain, and are thus promising for wide applications in nanoelectronics.