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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

cond-mat.dis-nnarXiv:cond-mat/0511479

Abstract

THz spectroscopy is used to identify a broad distribution of two-level systems, characteristic of glasses, in the substitutional monatomic mixed crystal systems, Ba1-xCaxF2 and Pb1-xCaxF2. In these minimally disordered systems, two-level behavior begins at a specific CaF2 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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