Thallium NMR study of the chain semiconductor TlS

We report an NMR study of electronic structure and wave functions overlap in the chain modification of semiconductor TlS which comprises two kinds of Tl atoms, Tl¹⁺ and Tl³⁺, residing in neighboring chains. Both univalent and trivalent Tl atoms show essential chemical shielding anisotropy despite of their 5d¹⁰ 6s² and 5d¹⁰ electron configurations. Such a behavior, along with the significant indirect exchange coupling of thallium nuclei obtained in our experiment, results from sp-hybridization of Tl electron wave functions and their overlap across the intervening S atoms. The aforementioned wave function overlap is expected to be the dominant mechanism in the formation of the valence and conduction bands in TlS and to determine the electronic structure of the compound.