Excitation of Hydrogen Motion inside a Nickel Vacancy

By means of the ion-channeling technique, we have shown the existence of a very low-energy ({~}3 meV) excitation for deuterium impurities trapped to vacancies in nickel. The excitation is associated with a change of the D location from near octahedral to near tetrahedral. On the basis of calculations of the D potentials within the effective-medium theory and the quantum treatment of the D motion, we suggest that the observed state can be regarded as an excited standing wave of a particle (D) on a sphere (internal surface around the vacancy).