Comparative critical field study of superconducting ternary borides

The upper critical field (Hc2) and electrical transport properties have been determined for ternary rare-earth transition-metal borides with a variety of crystal structures; namely, ScRu4B4 (I41/acd), LuRh4B4 (I41/acd), ThRh4B4 (P42/nmc), LuOs3B2 (P6/mmm), LuRuB2 (Pnma), and YRuB2 (Pnma). For the majority of the compounds the critical field measurements are analyzed in terms of the dirty limit [ltr/ξBCS(0)≪1] theory of Werthamer, Helfand, and Hohenberg (WHH). For the superconductor YRuB2, which is in the clean limit, critical field data are analyzed in terms of the Ginzburg-Landau theory. From the experimental data for\(({{dH_{c2} } \mathord{\left/ {\vphantom {{dH_{c2} } {dT}}} \right. \kern-\nulldelimiterspace} {dT}})_{T = T_c } \),Tc, and residual resistivity ρres, we also have determined the heat capacity coefficient γ and BCS coherence length ξBCS(0). The κ values indicate that these compounds are all strong type II superconductors.