Thermal Expansion of Vitreous Silica at Low Temperatures

Abstract

Measurements of the linear expansion coefficient $\ensuremath{\alpha}$ of pure vitreous silicas and ULE (Corning) silica at liquid-helium temperatures indicate a linear term analogous to that observed in the specific heat of glasses. This term, $x\ensuremath{\approx}\ensuremath{-}0.10\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}T$ ${\mathrm{K}}^{\ensuremath{-}1}$, leads to a large Gr\"uneisen parameter $\ensuremath{\gamma}$ between - 40 and - 50, suggestive of a tunneling process.