Prediction and Observation of Intermodulation Sidebands from Anharmonic Phonons

A quantum Langevin model, similar to models used recently for optomechanics, was used to predict intermodulation phonon sidebands (IPS). Ab initio calculations of anharmonic phonons in rocksalt NaBr showed these spectral features as "many-body effects". Modern inelastic neutron scattering...

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Bibliographic Details
Published in:arXiv.org 2021-01
Main Authors: Shen, Y, Saunders, C N, Bernal, C M, Abernathy, D L, Williams, T J, Manley, M E, Fultz, B
Format: Article
Language:English
Subjects:
Acoustic noise
Anharmonicity
Inelastic scattering
Intermodulation
Lattice vibration
Neutron scattering
Neutrons
Opto-mechanics
Phonons
Sidebands
Spectra
Thermal baths
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Summary:A quantum Langevin model, similar to models used recently for optomechanics, was used to predict intermodulation phonon sidebands (IPS). Ab initio calculations of anharmonic phonons in rocksalt NaBr showed these spectral features as "many-body effects". Modern inelastic neutron scattering measurements on a crystal of NaBr at 300K revealed diffuse intensity at high phonon energy from a predicted upper IPS. The transverse optical (TO) part of the new features originates from phonon intermodulation between the transverse acoustic (TA) and TO phonons. The longitudinal optical (LO) spectral features originate from three-phonon coupling between the TA modes and the TO lattice modes. The partner lower IPS proves to be an "intrinsic localized mode". Interactions with the thermal bath broaden and redistribute the spectral weight of the IPS pair. These sidebands are a probe of anharmonicity and quantum noise, which originate from interactions between the phonons in NaBr.
ISSN:2331-8422
DOI:10.48550/arxiv.2011.04842