Zusammenfassung
This work reports on four more Heusler superconductors: Pd(2)ZrAl,
Pd(2)HfAl, Pd(2)ZrIn, and Pd(2)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 Pd(2)B(1-x)B(x)(')Al, whereby B=Zr and Hf, and B(')=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.
