Electronic Band Structure Study of the Transport Properties of the Intermetallic Compounds ZrRuP and ZrRuSi

Electrical properties of the intermetallic superconductors h-ZrRuP, o-ZrRuP, and h-ZrRuSi were examined by calculating their electronic structures on the basis of the extended Hückel tight-binding method. To a first approximation, the electronic structure of ZrRuP is well described in terms of the oxidation state Zr⁴⁺(RuP)^4-. This picture provides simple explanations for why both h-ZrRuP and o-ZrRuP have low N(E_f) values and why h-ZrRuP has a nearly half-filled one-dimensional (1D) band dispersive along the c direction. A charge density wave instability associated with such a 1D band probably causes a c-axis doubling structural distortion in h-HfRuAs and h-TiRuAs. We discussed probable reasons for why the intermetallic phases with the c-axis doubling distortion are not superconductors and why h-ZrRuP has a higher T_c than does o-ZrRuP.