Optical Anisotropy in Tellurene and its Janus Allotropes -- A first principle Study

Here, we present first principle study of structural, electronic, and optical properties of pristine and janus tellurene allotropes using density functional theory (DFT). The $\alpha$, $\beta$, $\delta$, and $\eta$ allotrope of pristine tellurene exhibit indirect band gap while $\gamma$ and $\sigma$ allotropes are metallic. The bandgap shows tunability in janus tellurene compared to pristine tellurene. A metallic to semiconductor transition occurs in janus $\gamma$, $\sigma$ and its allotropes. Dirac cone-like interesting feature has been observed for pristine $\sigma$ tellurene which remains preserved with the opening in energy gap for janus allotrope. In optical properties, imaginary part dielectric function and electron energy loss spectra show a blue shift in janus tellurene as compared to pristine form. Static dielectric constant is tunable in janus tellurene. All allotropes of tellurene are optically active in UV-Vis region with optical anisotropy in all three directions. We believe that our findings will provide useful pointers in the experimental fabrication of devices based on janus tellurene.