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Glasslike two-level systems in minimally disordered mixed crystals.
J P Wrubel1, B E Hubbard, N I Agladze
1Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501, USA.
Physical Review Letters
|June 29, 2006
Summary
Terahertz (THz) spectroscopy revealed two-level systems in mixed crystals like BaCaF2 and PbCaF2. This previously unknown behavior emerges at specific calcium fluoride concentrations, suggesting collective dopant tunneling.
Area of Science:
- Solid-state physics
- Materials science
- Spectroscopy
Background:
- Glasses exhibit two-level systems (TLS) due to disorder.
- Substitutional monatomic mixed crystals offer minimally disordered systems for study.
- The presence of TLS in such systems was previously unknown.
Purpose of the Study:
- To investigate the presence and origin of two-level systems in Ba(1-x)Ca(x)F2 and Pb(1-x)Ca(x)F2 mixed crystals.
- To understand the concentration dependence of TLS emergence.
- To elucidate the underlying mechanism responsible for TLS in these systems.
Main Methods:
- Terahertz (THz) spectroscopy was employed to probe the systems.
- Analysis of the concentration dependence of observed phenomena.
- Modeling using the statistics of impurity distribution within the crystal lattice.
Main Results:
- A broad distribution of two-level systems, characteristic of glasses, was identified.
- Two-level behavior was observed to initiate at a specific CaF2 concentration in these minimally disordered systems.
- The concentration dependence of TLS was successfully modeled, aligning with impurity distribution statistics.
Conclusions:
- The study demonstrates the occurrence of glass-like two-level systems in specific mixed crystal compositions.
- A collective dopant tunneling mechanism is proposed as the cause for the observed two-level behavior.
- This finding expands the understanding of disorder-induced phenomena in crystalline solids.