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Glass-like two-level systems in minimally disordered mixed crystals

J. P. Wrubel·B. E. Hubbard·N. I. Agladze·A. J. Sievers·P. P. Fedorov·D. I. Klimenchenko·A. I. Ryskin·J. A. Campbell
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Abstract

THz spectroscopy is used to identify a broad distribution of two-level systems, characteristic of glasses, in the substitutional monatomic mixed crystal systems, Ba_{1-x}Ca_xF_2 and Pb_{1-x}Ca_xF_2. In these minimally disordered systems, two-level behavior begins at a specific CaF_2 concentration. The concentration dependence, successfully modeled using the statistics of the impurity distribution in the lattice, points to a collective dopant tunneling mechanism.

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J. P. Wrubel, B. E. Hubbard, N. I. Agladze, A. J. Sievers, P. P. Fedorov, D. I. Klimenchenko, A. I. Ryskin, J. A. Campbell. 2005-11-21. Glass-like two-level systems in minimally disordered mixed crystals. https://doi.org/10.1103/physrevlett.96.235503

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