Band Structure Studies of the R(5)Rh(6)Sn(18) (R = Sc, Y, Lu) Quasiskutteridite Superconductors

We report on X-ray photoelectron spectroscopy and ab initio electronic structure investigations of the skutterudite-related [Formula: see text] Rh [Formula: see text] Sn [Formula: see text] superconductors, where R = Sc, Y, and Lu. These compounds crystallise with a tetragonal structure (space group I [Formula: see text]) and are characterised by a deficiency of R atoms in their formula unit ([Formula: see text] Rh [Formula: see text] Sn [Formula: see text] , [Formula: see text]). Recently, we documented that the vacancies [Formula: see text] and atomic local defects (often induced by doping) are a reason for the enhancement in the superconducting transition temperature [Formula: see text] of these materials, as well as metallic ([Formula: see text]) or semimetallic ([Formula: see text]) behaviours in their normal state. Our band structure calculations show the pseudogap at a binding energy of −0.3 eV for the stoichiometric compounds, which can be easily moved towards the Fermi level by vacancies [Formula: see text]. As a result, dychotomic nature in electric transport of [Formula: see text] Rh [Formula: see text] Sn [Formula: see text] (metallic or semimetallic resistivity) depends on [Formula: see text] , which has not been interpreted before. We have shown that the densities of states are very similar for various [Formula: see text] Rh [Formula: see text] Sn [Formula: see text] compounds, and they practically do not depend on the metal R, while they are determined by the Rh d-and Sn s- and p-electron states. The band structure calculations for Sc [Formula: see text] Rh [Formula: see text] Sn [Formula: see text] have not been reported yet. We also found that the electronic specific heat coefficients [Formula: see text] for the stoichiometric samples were always larger with respect to the [Formula: see text] of the respective samples with vacancies at the R sites, which correlates with the results of ab initio calculations.