The boson peak (BP), a low-energy excess in the vibrational density of states over the Debye contribution, is often identified as a characteristic of amorphous solid materials. Despite decades of efforts, its microscopic origin still remains a mystery. Recently, it has been proposed, and corroborated with simulations, that the BP might stem from intrinsic localized modes involving one-dimensional (1D) string-like excitations (“stringlets”). We build on a theory originally proposed by Lund that describes the localized modes as 1D vibrating strings, but we specify the stringlet size distribution to be exponential, as observed in simulations. We provide an analytical prediction for the BP frequency ωBP in the temperature regime well below the observed glass transition temperature Tg. The prediction involves no free parameters and accords quantitatively with prior simulation observations in 2D and 3D model glasses based on inverse power law potentials. The comparison of the string model to observations is more uncertain when compared to simulations of an Al–Sm metallic glass material at temperatures well above Tg. Nonetheless, our stringlet model of the BP naturally reproduces the softening of the BP frequency upon heating and offers an analytical explanation for the experimentally observed scaling with the shear modulus in the glass state and changes in this scaling in simulations of glass-forming liquids. Finally, the theoretical analysis highlights the existence of a strong damping for the stringlet modes above Tg, which leads to a large low-frequency contribution to the 3D vibrational density of states, observed in both experiments and simulations.
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7 June 2024
Research Article|
June 04 2024
Stringlet excitation model of the boson peak
Special Collection:
2024 JCP Emerging Investigators Special Collection
Cunyuan Jiang
;
Cunyuan Jiang
(Formal analysis, Investigation, Methodology)
1
School of Physics and Astronomy, Shanghai Jiao Tong University
, 200240 Shanghai, China
2
Wilczek Quantum Center, Shanghai Jiao Tong University
, 200240 Shanghai, China
3
Shanghai Research Center for Quantum Sciences
, 200240 Shanghai, China
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Matteo Baggioli
;
Matteo Baggioli
a)
(Conceptualization, Investigation, Project administration, Resources, Writing – original draft)
1
School of Physics and Astronomy, Shanghai Jiao Tong University
, 200240 Shanghai, China
2
Wilczek Quantum Center, Shanghai Jiao Tong University
, 200240 Shanghai, China
3
Shanghai Research Center for Quantum Sciences
, 200240 Shanghai, China
a)Author to whom correspondence should be addressed: [email protected]
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Jack F. Douglas
Jack F. Douglas
(Conceptualization, Investigation, Writing – review & editing)
4
Materials Science and Engineering Division, National Institute of Standards and Technology
, Gaithersburg, Maryland 20899, USA
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Cunyuan Jiang
1,2,3
Matteo Baggioli
1,2,3,a)
Jack F. Douglas
4
1
School of Physics and Astronomy, Shanghai Jiao Tong University
, 200240 Shanghai, China
2
Wilczek Quantum Center, Shanghai Jiao Tong University
, 200240 Shanghai, China
3
Shanghai Research Center for Quantum Sciences
, 200240 Shanghai, China
4
Materials Science and Engineering Division, National Institute of Standards and Technology
, Gaithersburg, Maryland 20899, USA
a)Author to whom correspondence should be addressed: [email protected]
J. Chem. Phys. 160, 214505 (2024)
Article history
Received:
March 25 2024
Accepted:
May 20 2024
Citation
Cunyuan Jiang, Matteo Baggioli, Jack F. Douglas; Stringlet excitation model of the boson peak. J. Chem. Phys. 7 June 2024; 160 (21): 214505. https://doi.org/10.1063/5.0210057
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