Dielectric Constant of Glasses: Evidence for Dipole-Dipole Interactions

Abstract

The 1 kHz real part ${\ensuremath{\chi}}^{\ensuremath{'}}$ of the dielectric constant of a structural glass ($a\mathrm{\text{\ensuremath{-}}}{\mathrm{S}\mathrm{i}\mathrm{O}}_{2+x}{\mathrm{C}}_{1+y}{\mathrm{H}}_{z}$) was measured at low temperature $T$. Reducing the sample thickness $h$ below 100 nm weakens the slope $|\ensuremath{\partial}{\ensuremath{\chi}}^{\ensuremath{'}}/\ensuremath{\partial}T|$ for $T\ensuremath{\lesssim}0.1\text{ }\text{ }\mathrm{K}$, for all measuring fields $E$. This contrasts with the predictions of the two-level system (TLS) model but is in agreement with the recently proposed delocalization of excitations derived from a field-induced TLS-TLS interaction mechanism. For small $h$ this interaction is screened, which explains the $h$ effects on ${\ensuremath{\chi}}^{\ensuremath{'}}$. Hence, interactions must play a key role in standard thick samples as soon as $T\ensuremath{\lesssim}0.1\text{ }\text{ }\mathrm{K}$.