Optical signature of flat bands in topological hourglass semimetal Nb₃SiTe₆

Flat electronic bands in condensed matter provide a rich avenue for exploring novel quantum phenomena. Here, we report an optical spectroscopy study of a topological hourglass semimetal Nb₃SiTe₆ with the electric field of the incident light parallel to its crystalline ab-plane. The ab-plane optical conductivity spectra of Nb₃SiTe₆ single crystals exhibit a remarkable peak-like feature around 1.20 eV, which is mainly contributed by the direct optical transitions between the two ab-initio-calculation-derived flat bands along the momentum direction Z–U. Our results pave the way for investigating exotic quantum phenomena based on the flat bands in topological hourglass semimetals.