This work reports on four more Heusler superconductors: ${\text{Pd}}_2\text{ZrAl}$, ${\text{Pd}}_2\text{HfAl}$, ${\text{Pd}}_2\text{ZrIn}$, and ${\text{Pd}}_2\text{HfIn}$. These compounds exhibit superconducting transition temperatures ranging from 2.4–3.8 K as determined by resistivity measurements. According to their behavior in an external magnetic field, all compounds are type II bulk superconductors. The occurrence of superconductivity was predicted for these compounds using electronic structure calculations. The electronic structures exhibit van Hove singularities (saddle points) at the $L$ point. These lead to a maximum in the corresponding density of states and superconductivity according to the van Hove scenario. The superconducting properties of electron-doped and hole-doped substituted compounds ${\text{Pd}}_2{B}_{1-x}{B}_x^{\prime }\text{Al}$, whereby $B=\text{Zr}$ and Hf, and $B^{\prime }=\text{Y}$, Nb, and Mo, were investigated to obtain information about the dependence of the transition temperature on the density of states at the Fermi energy following the van Hove scenario. The calculated electronic structure reveals that the substituted compounds do not follow a rigid-band model. In addition, the random distribution of the substituted atoms strongly increases impurity-type electron scattering. The substituent concentrations used in this work lead to strongly enhanced impurity-type scattering and eventually to suppression of the superconducting state.

• Received 5 September 2008

DOI:https://doi.org/10.1103/PhysRevB.79.064508