Indirect nuclear exchange coupling and electronic structure of the layered semiconductorTlS: NMR study and band structure calculation

Abstract

We have studied the electronic structure of the layered semiconductor TlS by means of203Tl and 205Tl NMR and band structure calculation. The crystal structure of thiscompound is built from the metal–chalcogen layers formed of linkedTl3+S42− tetrahedraand Tl+ ions located between the layers. Our experiments show significant interlayer indirectexchange coupling of thallium nuclei. Since the distances between thallium ions essentiallyexceed the sum of their ionic radii, it is concluded that such coupling is realized due to theoverlap of the Tl electron wavefunctions across the intervening S atom. The exchangeinteraction has been evaluated by means of the quantitative spectral analysis. The bandstructure calculation shows that the top of the valence band is composed of mixedTl+ 6s6pz–S3s3pz–Tl3+ 6s6pz states, yieldingoverlap of the Tl+–S–Tl3+ type. Such electronic structure gives rise to the effective interlayer coupling ofTl nuclear spins observed in the experiment. This effect is discussed along withthe recently obtained NMR results in the chain thallium sulfide and selenide.