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
TL;DR
This study uses THz spectroscopy to reveal glass-like two-level systems in minimally disordered mixed crystals, showing that such behavior emerges at specific dopant concentrations and is modeled by impurity distribution statistics.
Contribution
It demonstrates the presence of glass-like two-level systems in minimally disordered crystals and introduces a collective dopant tunneling model based on impurity statistics.
Findings
Two-level systems appear at specific CaF_2 concentrations.
The behavior is modeled by impurity distribution statistics.
A collective dopant tunneling mechanism is proposed.
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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