Enhanced superconductivity in zirconium after H(D) implantation

Zirconium foils (superconducting transition atT _c =0.7 K) were implanted at liquid helium temperatures with hydrogen, deuterium and helium. In all cases a remarkable increase ofT _c was observed. Implantation of the inert He atoms leads only to the introduction of lattice defects, which is known to increaseT _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 theT _c increase to 1.49 K after He implantation, whereasT _c is even more enhanced by implantation of the hydrogen isotopes. The maximum values forT _c are 3.14 K for H and 4.65 K for D implantation. The concentration necessary to produce a saturation inT _c for both isotopes is H(D)/Zr0.13. The remarkably highT _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.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday