Magnetic field effect on the dielectric constant of glasses: Evidence of disorder within tunneling barriers

Abstract

The magnetic field dependence of the low-frequency dielectric constant ${\ensuremath{\epsilon}}_{r}(H)$ of a structural glass $a\ensuremath{-}{\mathrm{SiO}}_{2+x}{\mathrm{C}}_{y}{\mathrm{H}}_{z}$ was studied from 400 to 50 mK and for H up to $3 \mathrm{T}.$ Measurement of both the real and the imaginary parts of ${\ensuremath{\epsilon}}_{r}$ is used to eliminate the difficult question of keeping constant the temperature of the sample while increasing H: a nonzero ${\ensuremath{\epsilon}}_{r}(H)$ dependence is reported in the same range as that very recently reported on multicomponent glasses. In addition to the recently proposed explanation based on interactions, the reported ${\ensuremath{\epsilon}}_{r}(H)$ is interpreted quantitatively as a consequence of the disorder lying within the nanometric barriers of the elementary tunneling systems of the glass.