This title appears in the Scientific Report :
2007
Please use the identifier:
http://hdl.handle.net/2128/7733 in citations.
Please use the identifier: http://dx.doi.org/10.1103/PhysRevB.76.064206 in citations.
Vibrational instability, two-level systems, and the boson peak in glasses
Vibrational instability, two-level systems, and the boson peak in glasses
We show that the same physical mechanism is fundamental for two seemingly different phenomena such as the formation of two-level systems in glasses and the boson peak in the reduced density of low-frequency vibrational states g(omega)/omega(2). This mechanism is the vibrational instability of weakly...
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Personal Name(s): | Parshin, D. A. |
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Schober, H. R. / Gurevich, V. L. | |
Contributing Institute: |
Theorie der Strukturbildung; IFF-3 |
Published in: | Physical Review B Physical review / B, 76 76 (2007 2007) 6 6, S. 064206 064206 |
Imprint: |
College Park, Md.
APS
2007
|
Physical Description: |
064206 |
DOI: |
10.1103/PhysRevB.76.064206 |
Document Type: |
Journal Article |
Research Program: |
Kondensierte Materie |
Series Title: |
Physical Review B
76 |
Subject (ZB): | |
Link: |
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Publikationsportal JuSER |
Please use the identifier: http://dx.doi.org/10.1103/PhysRevB.76.064206 in citations.
We show that the same physical mechanism is fundamental for two seemingly different phenomena such as the formation of two-level systems in glasses and the boson peak in the reduced density of low-frequency vibrational states g(omega)/omega(2). This mechanism is the vibrational instability of weakly interacting harmonic modes. Below some frequency omega(c)<omega(0) (where omega(0) is of the order of Debye frequency), the instability, controlled by the anharmonicity, creates a new stable universal spectrum of harmonic vibrations with a boson peak feature as well as double-well potentials with a wide distribution of barrier heights. Both are determined by the strength of the interaction I proportional to omega(c) between the oscillators. Our theory predicts in a natural way a small value for the important dimensionless parameter C=(P) over bar gamma(2)/rho v(2)approximate to 10(-4) for two-level systems in glasses. We show that C approximate to(W/h omega(c))(3)proportional to I-3 and decreases with increasing interaction strength I. The energy W is an important characteristic energy in glasses and is of the order of a few Kelvin. This formula relates the two-level system's parameter C with the width of the vibration instability region omega(c), which is typically larger or of the order of the boson peak frequency omega(b). Since h omega(c)greater than or similar to h omega(b)> W, the typical value of C and, therefore, the number of active two-level systems is very small, less than 1 per 1x10(7) of oscillators, in good agreement with experiment. Within the unified approach developed in the present paper, the density of the tunneling states and the density of vibrational states at the boson peak frequency are interrelated. |