Motion of interstitials in metals: Quantum tunneling at low temperatures

Tunneling rates for heavy-impurity interstitials in fcc metals are calculated. The full interstitial---host-lattice coupling is taken into account in the dynamics as well as in the lattice relaxation. It is shown that resonant modes play a decisive role in tunneling. The results of this full dynamical study are compared to simple one-dimensional models, from which it appears that the one-dimensional approximation can be used to extrapolate to different values of mass, jump distance, and classical activation energy. The method can be extended to study the finite-temperature behavior, and we indicate how this can be done.