Nonadiabatic Low-Temperature Quantum Diffusion of Hydrogen in Nb(OH) _<i>x</i>

Abstract

The local jump diffusion of trapped H in two Nb(OH)x samples was investigated between 10 and 160 K by neutron spectroscopy. The jump rates vary by less than a factor of 7. Below ∼ 70 K, they exhibit Kondo's T2K-1 temperature power law for a diffusion process that is controlled by nonadiabatic coupling to conduction electrons. Above ∼ 70 K, the diffusion is dominated by the interaction with phonons.