Strongly Anisotropic Strain-Tunability of Excitons in Exfoliated ZrSe₃

The effect of uniaxial strain on the band structure of ZrSe₃ , a semiconducting material with a marked in-plane structural anisotropy, is studied. By using a modified three-point bending test apparatus, thin ZrSe₃ flakes are subjected to uniaxial strain along different crystalline orientations monitoring the effect of strain on their optical properties through micro-reflectance spectroscopy. The obtained spectra show excitonic features that blueshift upon uniaxial tension. This shift is strongly dependent on the direction along which the strain is being applied. When the flakes are strained along the b-axis, the exciton peak shifts at ≈60-95 meV %^-1 , while along the a-axis, the shift only reaches ≈0-15 meV %^-1 . Ab initio calculations are conducted to study the influence of uniaxial strain, applied along different crystal directions, on the band structure and reflectance spectra of ZrSe₃ , exhibiting a remarkable agreement with the experimental results.