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

The magnetic field dependence of the low-frequency dielectric constant epsilon(r)(H) of a structural glass a-SiO2+xCyHz was studied from 400 to 50 mK and for H up to 3 T. Measurement of both the real and the imaginary parts of epsilon(r) is used to eliminate the difficult question of keeping constant the temperature of the sample while increasing H: a nonzero 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 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.