Evidence for a two-component tunnelling mechanism in the multicomponent glasses at low temperatures

The thermal and dielectric anomalies of window-type glasses at low temperatures (T < 1 K) are somewhat successfully explained by the two-level systems (2LS) tunneling model (TM). However, the magnetic effects discovered in the multisilicate glasses in recent times, and also some unexplained older data in zero magnetic field for the mixed (SiO2)(1-x)(K2O)(x) and (SiO2)(1-x)(Na2O)(x) glasses, indicate the need for a suitable generalization of this standard model. We present evidence that also for the mixed glasses in the absence of a field the right extension of the 2LS TM is provided by the multilevel (anomalous) tunneling systems approach proposed by one of us to explain the magnetic effects. It appears that new 2LS develop via dilution near the hull of the SiO4-percolating clusters in the mixed glasses.