Strain dependence of photoluminescence and circular dichroism in transition metal dichalcogenides: a k.p analysis

Within a two-band $k\cdot p$ method we analyze different types of strain for the $K$ valley optical characteristics of a freestanding monolayer MoS$_2$, MoSe$_2$, WS$_2$ and WSe$_2$. We predict that circular polarization selectivity for energies above the direct transition onset deteriorates/improves by tensile/compressive strain. Wide range of available strained-sample photoluminescence data can be reasonably reproduced by this simple bandstructure combined with accounting for excitons at a variational level. According to this model strain impacts optoelectronic properties through its hydrostatic component, whereas the shear strain only causes a rigid wavevector shift of the valley. Furthermore, under the stress loading of flexible substrates the presence of Poisson's effect or the lack of it are examined individually for the reported measurements.