  Using first-principles calculations, we systematically investigate the
electronic structures and band topologies of four kinds of group-V elemental
(P, As, Sb and Bi) monolayers with buckled honeycomb structure. It is found
that all these monolayers can change from semiconducting to semimetallic under
compressive strain. If a tensile strain is however applied, the P, As and Sb
monolayers undergo phase transition from topologically trivial to non-trivial
regime, whereas the topological insulating nature of Bi monolayer remains
unchanged. With tunability of the band gaps and band topologies, it can be
expected that these elemental monolayers could be promising candidates for
future optoelectronic and spintronic applications.
