Theory of quantum diffusion in solid hydrogen. I. New type of stimulation of tunneling mobility
Abstract
Quantum diffusion in a system of self-localizing narrow-band particles is studied taking into account the time varying energy shift created by the impurity environment. This effect is most strongly manifested in the case when the particles creating the shift have internal degrees of freedom which interact strongly with phonons. A general formula is obtained for the quantum-diffusion mobility taking into account coherent two-phonon (Γ) and fluctuation (γ) broadening, as well as the random static shift ϕ. At low temperatures (Γ ≪ γ) the fluctuation shift often (for example, in solid hydrogen) turns out to be the most significant factor, giving rise to delocalization of the impurities. In the limit ϕ, γ →0, the expressions obtained in the limiting cases transform into well-known formulas from the Kagan-Maksimov theory of quantum diffusion.