  When the dimension of a solid structure is reduced, there will be two
emerging effects, quantum confinement and surface effect, which dominate at
nanoscale. Based on first-principles calculations, we demonstrate that due to
an intriguing interplay between these two dominating effects, the topological
and electronic (topo-electronic) properties of Sb (111) nanofilms undergo a
series of transitions as a function of the reducing film thickness:
transforming from a topological semimetal to a topological insulator at 7.8 nm
(22 bilayer), then to a quantum spin hall (QSH) phase at 2.7 nm (8 bilayer),
and finally to a normal (topological trivial) semiconductor at 1.0 nm (3
bilayer). Our theoretical findings for the first time identify the existence of
the QSH in the Sb (111) nanofilms within a narrow range of thickness and
suggest that the Sb (111) nanofilms provide an ideal test bed for experimental
study of topo-electronic phase transitions.
