Critical Points in the Dielectric Function Spectra of the TlInSe2 and TlInTe2 Ternary Chain Compounds

The first spectro-ellipsometric study of TlInSe₂ and TlInTe₂ is performed at room temperature. The obtained spectra of the dielectric function are analysed in terms of standard analytic line shapes and are separated into contributions from the different interband critical points. The interpretation is done in terms of band structure of TISe (TlTlSe₂), a binary prototype of TlInSe₂ and TlInTe₂. The results of line shape analysis for TISe are also given.