Low-temperature specific heat and thermal conductivity of neutron-irradiated crystalline quartz

Abstract

The specific heat $C$ and thermal conductivity $\ensuremath{\kappa}$ of neutron-irradiated crystalline quartz have been measured to \ensuremath{\lesssim}0.1 K. Four types of low-energy excitations are observed, two of which may be removed selectively by heat treatment. From the $C$ and $\ensuremath{\kappa}$ of annealed samples it is shown that the localized excitations found in vitreous silica also occur in neutron-damaged quartz. These excitations cause the unusual low-temperature behavior which is characteristic of amorphous materials. The properties of these excitations appear to remain unchanged as the total density of excitations is reduced by a factor of \ensuremath{\approx} 40. At greater dilution, the localized excitations are masked by the effects of other, unidentified excitations.