  Using the tight-binding (TB) approximation with inclusion of the spin-orbit
interaction, we predict a topological phase transition in the electronic band
structure of phosphorene in the presence of axial strains. We derive a
low-energy TB Hamiltonian that includes the spin-orbit interaction for bulk
phosphorene. Applying a compressive biaxial in-plane strain and perpendicular
tensile strain in ranges where the structure is still stable leads to a
topological phase transition. We also examine the influence of strain on zigzag
phosphorene nanoribbons (zPNRs) and the formation of the corresponding
protected edge states when the system is in the topological phase. For zPNRs up
to a width of 100 nm the energy gap is at least three orders of magnitude
larger than the thermal energy at room temperature.
