Two Gaps in Semiconducting EuSbTe_3 Studied by Angle-Resolved Photoemission Spectroscopy

Using angle-resolved photoemission spectroscopy, we study the low-energy electronic structure of a layered ternary telluride EuSbTe_3 semiconductor. It is found that the photoemission constant energy contours can be well described by the simple two-parameter (t_\rm perp and t_\rm para) tight-binding model based on the Te orbitals in square-net planes of EuSbTe_3, suggesting its Te 5p orbitals dominated low-lying electronic structure, which is reminiscent of other rare-earth tritellurides. However, a possible charge-density-wave gap of 80 meV is found to persist in 300 K, which renders the unexpected semiconducting properties in EuSbTe_3. Moreover, we reveal an extra band gap occurring around 200 meV below the Fermi level at low temperatures, which can be attributed to the interaction between the main and folded bands due to lattice scatterings. Our findings provide the first comprehensive understanding of the electronic structure of layered ternary tellurides, which lays the basis for future research on these compounds.