Strain-Tuned Optical Properties of a Two-Dimensional Hexagonal Lattice: Exploiting Saddle Degrees of Freedom and Saddle Filtering Effects

The deformation of hexagonal lattices has attracted considerable attention due to its promising applications in straintronics. This study employs the tight-binding model to investigate the anisotropic spectrum, where electronic transport can be manipulated by the degree of deformation. The longitudinal conductivities, light transmittance, and absorbance are analyzed, revealing enhancement along one direction and suppression along the other. The findings indicate that the direction and magnitude of strain can be determined by measuring transmittance and absorbance, showing significant deviations from the unstrained condition. Furthermore, a strong absorbance is observed due to the interband transition of electrons near the M-point saddles, linked to van Hove singularities for specific values of nearest and next-nearest hoping energy. The unexpected characteristics of saddle polarization-analogous to valley polarization at K- and K'-become particularly prominent when strain affects the selection of M-point saddle. Notably, the demonstration indicates that a highly efficient M-point saddle filtering effect takes place, induced by linearly polarized light. This model paves the way for exploring the optical properties of anisotropic hexagonal lattices, such as black phosphorus and borophene oxide. These results also open a pathway to strain-programmable optoelectronic devices, such as polarization-selective photodetectors, tunable absorbers, and ultrathin optical filters.