Abstract
The thermal and dielectric anomalies of window-type glasses at low temperatures (T < 1 K) are rather successfully explained by the two-level systems (2LS) standard tunneling model (STM). However, the magnetic effects discovered in the multisilicate glasses in recent times, magnetic effects in the organic glasses, and also some older data from mixed (SiO2)1−x(K2O)x and (SiO2)1−x(Na2O)x glasses indicate the need for a suitable extension of the 2LS-STM. We show that—not only for the magnetic effects, but also for the mixed glasses in the absence of a field—the right extension of the 2LS-STM is provided by the (anomalous) multilevel tunnelling systems (ATS) proposed by one of us for multicomponent amorphous solids. Though a secondary type of TS, different from the standard 2LS, was invoked long ago already, we clarify their physical origin and mathematical description and show that their contribution considerably improves the agreement with the experimental data. In spite of dealing with low-temperature properties, our work impinges on the structure and statistical physics of glasses at all temperatures.
Highlights
Glasses are ubiquitous materials of considerable importance for many practical applications; for physicists the nature of the glass transition and the ultimate microscopic structure of glasses determining their physical properties remain to this day issues of considerable intellectual challenge [1]
The magnetic effects discovered in the multisilicate glasses in recent times, magnetic effects in the organic glasses, and some older data from mixed (SiO2)1−x(K2O)x and (SiO2)1−x(Na2O)x glasses indicate the need for a suitable extension of the 2welled potentials (2LS)-standard tunneling model (STM)
We show that— for the magnetic effects, and for the mixed glasses in the absence of a field—the right extension of the 2LS-STM is provided by the multilevel tunnelling systems (ATS) proposed by one of us for multicomponent amorphous solids
Summary
Glasses are ubiquitous materials of considerable importance for many practical applications; for physicists the nature of the glass transition and the ultimate microscopic structure of glasses determining their physical properties remain to this day issues of considerable intellectual challenge [1]. Magnetic effects have been reported for both the real and imaginary part of ε at low frequency (ω ∼ 1 kHz), for the heat capacity Cp (see, e.g., [21]) and for the polarization echo (where changes in the presence of a magnetic field have been the strongest [10,11,12]) as well This behavior was confirmed in other multicomponent glasses, like borosilicate optical glass BK7 and commercial Duran [8], and, similar effects on ε(T) have been confirmed in studies of the structural glass a-SiO2+xCyHz in the range 50 < T < 400 mK and B ≤ 3T [9]. A short preliminary account of this work was published in [22]
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