Low Temperature Physics: 29, 373 (2003); https://doi.org/10.1063/1.1542499 (5 pages)
Fizika Nizkikh Temperatur: Volume 29, Number 5 (May 2003), p. 501-507    ( to contents , go back )

Diffusion of a probe nanoparticle in a quantum crystal with narrow vacancy band

A.A. Levchenko, L.P. Mezhov-Deglin, and A.B. Trusov

Institute of Solid State Physics of Russian Academy of Sciences, Chernogolovka, Moscow district, 142432, Russia
E-mail: mezhov@issp.ac.ru
pos Анотація:

Received January 8, 2003

Abstract

The vacancy-assisted diffusion of a probe nanoparticle with a diameter dp of a few nm drifting through a quantum crystal with a narrow vacancy band Qv << Tmelt is considered qualitatively. Below the melting point Tmelt the temperature dependence of the diffusion coefficient of the nanoprobe, Dp(T), changes significantly at temperatures near Ttr (TmeltTtrQv), where the transition from thermally activated hopping of localized vacancies to a proper band motion of delocalized vacancions takes place. Moreover, if the mean free path of the vacancions lv(T) at Ttr is less than dp and increases with lowering temperature quicker than xv-1 (here xv is the relative concentration of the thermal vacancies) the diffusion coefficient Dp of the nanoprobe drifting in the dense gas of quasiparticles grows with cooling the sample. At T << Ttr, in the rarified gas of quasiparticles where lv >> dp, the diffusion coefficient Dp falls almost near exponentially, proportionally with xv, if the cross-section of inelastic vacancion-probe particle scattering is weakly dependent on temperature. We believe that our model could be applied for the description of the diffusion of positive charges in hcp 4He crystals grown at pressures higher than the minimal pressure of helium solidification and the diffusion of negative charges in hcp crystals grown from pure parahydrogen.

PACS:
67.80.-s - Solid helium and related quantum crystals

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