  We report on the preparation and the physical properties of superconducting
(TaNb)_1-x(ZrHfTi)_x high-entropy alloy films. The films were prepared by means
of magnetron sputtering at room temperature, with x ranging from 0 to 1 with an
average thickness of 600 - 950 nm. All films crystallize in a pseudo
body-centered cubic (BCC) structure. For samples with x < 0.65, the
normal-state properties are metallic, while for x > 0.65 the films are weakly
insulating. The transition from metallic to weakly insulating occurs right at
the near-equimolar stoichiometry. We find all films, except for x = 0 or 1, to
become superconducting at low temperatures, and we interpret their
superconducting properties within the Bardeen-Cooper-Schrieffer (BCS)
framework. The highest transition temperature T_c = 6.9 K of the solid solution
is observed for x = 0.43. The highest upper-critical field B_c2(0) = 11.05 T is
found for the near-equimolar ratio x = 0.65, where the mixing entropy is the
largest. The superconducting parameters derived for all the films from
transport measurements are found to be close to those that are reported for
amorphous superconductors. Our results indicate that these films of
high-entropy alloys are promising candidates for superconducting device
fabrication.
