Polarized Infrared Spectroscopy of FeTe₂ Single Crystals

There is renewed interest in thermoelectric performances of transition metal dichalcogenides (FeTe₂, FeS₂, FeSe₂), and in their potential for optoelectronics applications, as they are narrow gap semiconductors with large electron mobility and strong absorption in visible/ultraviolet spectral regions. With the goal of addressing some of the open questions regarding their electronic properties, we performed measurements of polarized infrared reflectance on single crystals of FeTe₂, focusing in particular on samples with vacancy defects, which were found to suppress long range magnetic order. Here, we discuss the in-plane anisotropy of optical conductivity and optical band gap, as well as additional optical transitions observed at low energies, below the gap. We show that our data is in good agreement with recent band structure calculations, indicating spin-splitting of the e_g and t_g orbitals of the Fe-3d shell.