Low-energy Excitations In Disordered Solids: A Story Of The 'Universal' Phenomena Of Structural Tunneling by Richard B Stephens;Xiao Liu;

Author:Richard B Stephens;Xiao Liu;
Language: eng
Format: epub
Publisher: World Scientific Publishing Company
Published: 2021-06-15T00:00:00+00:00

6.5.3. Defective crystals

Observation of crystalline ceramics, with grain sizes ≈100 nm and <10% amorphous, shows specific heat similar to glasses (Leadbetter et al., 1977; Collocott and White, 1990),35 but these materials are sufficiently complex that one cannot point to a specific source, or distinguish them from interfacial effects. It might be more informative to start with a perfect crystal (unlike the previous section) and add perturbations (point defects, dislocations, or grain boundaries) to see when/if glassy states arise.36

Proper measurements of slightly defective crystals and understanding of them require very careful work. The current status is that losses in good crystals can be reduced to the point that only surface losses are apparent below a few K (Nawrodt et al., 2013; Metcalf et al., 2018), where phonon–phonon and thermoelastic losses are insignificant. What happens then when defects are introduced into crystal? Is there a critical concentration at which tunneling states appear?

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