Enhanced superconductivity in zirconium after H(D) implantation

Zirconium foils (superconducting transition at Tsub(c) = 0.7 K) were implanted at liquid helium temperatures with hydrogen, deuterium and helium. In all cases a remarkable increase of Tsub(c) was observed. Implantation of the inert He atoms leads only to the introduction of lattice defects, which is known to increase Tsub(c) of Zr. However, the implanted H and D atoms exert an additional influence on the superconducting behavior based on a change of the electronic properties and an increase of the electron-phonon coupling. Introduction of lattice defects seems to account for the Tsub(c) increase to 1.49 K after He implantation, whereas Tsub(c) is even more enhanced by implantation of the hydrogen isotopes. The maximum values for Tsub(c) are 3.14 K for H and 4.65 K for D implantation. The concentration necessary to produce a saturation in Tsub(c) for both isotopes is H(D)/Zr approx. 0.13. The remarkably high Tsub(c) for the heavier isotope corresponds to an extreme inverse isotope effect. A smaller inverse isotope effect was found earlier in the Pd-H(D) system, where it could be explained by anharmonic effects. (orig.)