  We study the effects of an applied in-plane uniaxial strain on the plasmon
dispersions of monolayer, bilayer and double-layer phosphorene structures in
the long-wavelength limit within the linear elasticity theory. In the low
energy limit, these effects can be modeled through the change in the curvature
of the anisotropic energy band along the armchair and zigzag directions. We
derive analytical relations for the plasmon modes under uniaxial strain and
show that the direction of the applied strain is important. Moreover, we
observe that along the armchair direction, the changes of the plasmon
dispersion with strain are different and larger than those along the zigzag
direction. Using the analytical relations for two-layer phosphorene systems, we
find that the strain-dependent orientation factor of layers could be considered
as a means to control the variations of the plasmon energy. Furthermore, our
study shows that the plasmonic collective modes are more affected when the
strain is applied equally to the layers compared to the case in which the
strain is applied asymmetrically to the layers. We also calculate the effect of
strain on the drag resistivity in a double-layer phosphorene structure and
obtain that the changes in the plasmonic excitations, due to an applied strain,
are mainly responsible for the predicted results. This study can be easily
extended to other anisotropic two-dimensional materials.
