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dc.contributor.advisorMetz, Andreas
dc.creatorAgyare, Benjamin Adu
dc.date.accessioned2020-10-20T13:33:15Z
dc.date.available2020-10-20T13:33:15Z
dc.date.issued2019
dc.identifier.urihttp://hdl.handle.net/20.500.12613/644
dc.description.abstractWe examined the formation of Intrinsically Localized Modes (ILMs) for a pair of harmonic phonons along the direction [111] of the Sodium Iodide (NaI) crystalline lattice. The tendency for ILMs to form at a certain center-of-mass momentum ▁q and corresponding relative momentum vector ▁k is attributed to the van-Hove singularities condition in the non-interaction two-phonon density of states continuum. We observed that, as ▁q converges to the high-symmetry point L=▁q (π/a,π/a,π/a) of the Brillouin zone, the relative momentum vector ▁k remains invariant at ▁k (π/2,π/2,π/2) for a certain threshold value of ▁q, and coalesces at the upper-edge of the two-phonon density of states spectrum with high degeneracy in the two-phonon critical energy. We conclude that the excitation spectra of the pairs of harmonic phonon excitations become energetically degenerate past the threshold ▁q value towards L at the invariant vector ▁k, announcing the strong presence of ILMs. The calculated ILMs were observed at critical energies of 20.0 meV and 25.0 meV for the spring coupling constants ratios K_2/K_1 ≈0.598 and K_2/K_1 ≈0.202 respectively. Reports of Inelastic Neutron Scattering experiments have identified one-phonon breather excitations energy of 10.2 meV at elevated temperatures of 555 K. The formation of ILMs, or multi-phonon bound states, is expected to arise as a result of the anharmonic interactions that lift these degeneracies to enhance the formation of ILMs.
dc.format.extent144 pages
dc.language.isoeng
dc.publisherTemple University. Libraries
dc.relation.ispartofTheses and Dissertations
dc.rightsIN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available.
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.subjectPhysics
dc.subjectPhysics, Condensed Matter
dc.subjectIlms
dc.subjectIntrinsic
dc.subjectLattice
dc.subjectModes
dc.subjectPhonons
dc.subjectVibrations
dc.titleIntrinsically Localized Lattice Vibrations in Crystalline Lattices
dc.typeText
dc.type.genreThesis/Dissertation
dc.contributor.committeememberPerdew, John P.
dc.contributor.committeememberWu, Xifan
dc.contributor.committeememberMatsika, Spiridoula
dc.description.departmentPhysics
dc.relation.doihttp://dx.doi.org/10.34944/dspace/626
dc.ada.noteFor Americans with Disabilities Act (ADA) accommodation, including help with reading this content, please contact scholarshare@temple.edu
dc.description.degreePh.D.
refterms.dateFOA2020-10-20T13:33:15Z


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