Multilevel Tunnelling Systems and Fractal Clustering in the Low-Temperature Mixed Alkali-Silicate Glasses

Figure 7

Dielectric signature of pure 𝑎-SiO₂ (inset) and AlBaSiO (main) glasses. SiO₂ data [53], fitted with (8), display a −2 : 1 2LS-TM behavior. AlBaSiO data [54] display rather a −1 : 1 behavior, yet could be fitted with (8) (dashed line) [54] with a large Δ_0min=12.2 mK 2LS tunneling parameter. We have fitted all data with a more realistic Δ_0min=3.9 mK and best fit parameters from Table 1 using (8) and (14) (driving frequency 𝜔=1 kHz).