  High-entropy alloys are made from random mixtures of principal elements on
simple lattices, stabilized by a high mixing entropy. The recently discovered
BCC Ta-Nb-Hf-Zr-Ti high entropy alloy superconductor appears to display
properties of both simple crystalline intermetallics and amorphous materials,
e.g. it has a well defined superconducting transition along with an exceptional
robustness against disorder. Here we show that the valence-electron count
dependence of the superconducting transition temperature in the high entropy
alloy falls between those of analogous simple solid solutions and amorphous
materials, and test the effect of alloy complexity on the superconductivity. We
propose high-entropy alloys as excellent intermediate systems for studying
superconductivity as it evolves between crystalline and amorphous materials.
