Multi-layered Chalcogenides with potential for magnetism and superconductivity

Layered thallium copper chalcogenides can form single, double, or triple layers of Cu–Ch separated by Tl sheets. Here we report on the preparation and properties of Tl-based materials of TlCu₂Se₂, TlCu₄S₃, TlCu₄Se₃ and TlCu₆S₄. Having no long-range magnetism for these materials is quite surprising considering the possibilities of inter- and intra-layer exchange interactions through Cu 3d, and we measure by magnetic susceptibility and confirm by neutron diffraction. First principles density-functional theory calculations for both the single-layer TlCu₂Se₂ (isostructural to the ‘122’ iron-based superconductors) and the double-layer TlCu₄Se₃ suggest a lack of Fermi-level spectral weight that is needed to drive a magnetic or superconducting instability. However, for multiple structural layers with Fe, there is much greater likelihood for magnetism and superconductivity.