Coherence – Interactions in nonlinear elastic media cause multiple scattering and resonances of sound waves, which lead to the loss of phase coherence and acoustic wave degradation through amplitude reduction. Unprecedented control of waste heat may be enabled by the design of media that make thermal phonons more coherent. This may lead to the energy available from current generation technologies being doubled by reduced loss to heat. By selectively tailoring the nature and magnitude of interactions through the supporting medium to control the level of coherence of sound waves, NewFoS research is developing strategies to overcome energy loss and dissipation in energy applications, or to increase dissipation when desired.

Recently, extraordinary modes of high frequency phonon transport have been demonstrated at room temperature. These include ballistic transport over distances of many microns, with significant contributions to thermal conductivity [1-3] and coherent propagation through phononic materials with numerous interfaces [4]. Coherent transport of high-frequency phonons across macroscopic distances was believed to be only possible at cryogenic temperatures where phonon–phonon scattering, the primary phonon decoherence mechanism, was minimized. These reports suggest it is possible to tailor new phenomena related to phonon scattering in the GHz-to-THz range at room temperature. In our laboratories, via microstructure we have demonstrated how to manage interactions between sound waves to enhance nonlinearity to create strong localization of modes such as solitary waves, which enforce long-range coherent energy propagation in highly nonlinear media [5-9].

Coherence: (A) Generating 2.5 THz coherent phonons in a laser-driven piezoelectric superlattice [60]. (B) Death-star femtosecond multiple-pulse generation for excitation of GHz-THz phonons [61]. (C) Coherent THz optic-phonon-polaritons in a periodically structured LiNbO3 crystal [62]. Images of the x-propagating wave were compressed in the y-direction with time order upward to show propagation in a single space-time illustration.

  1. T.K. Hsiao, H.K. Chang, S.C. Liou, M.W. Chu, S.C. Lee and C.W. Chang, “Observation of room-temperature ballistic thermal conduction persisting over 8.3 μm in SiGe nanowires,” Nature Nanotechnology 8, 534 (2013).
  2. I. Lisiecki, D. Polli, C. Yan, G. Soavi, E. Duval, G. Cerullo and M.P. Pileni, “Coherent Longitudinal Acoustic Phonons in Three-Dimensional Supracrystals of Cobalt Nanocrystals,” Nano Letters 13, 4914 (2013).
  3. J. Ravichandran, A.K. Yadav, R. Cheaito, P.B. Rossen, A. Soukiassian, S.J. Suresha, J.C. Duda, B.M. Foley, C.H. Lee, Y. Zhu, A.W. Lichtenberger, J.E. Moore, D.A. Muller, D.G. Schlom, P.E. Hopkins, A. Majumdar, R. Ramesh and M.A. Zurbuchen, “Crossover from incoherent to coherent phonon scattering in epitaxial oxide superlattices,” Nature Materials 13, 168 (2014).
  4. A.A. Maznev, F. Hofmann, A. Jandl, K. Esfarjani, M.T. Bulsara, E.A. Fitzgerald, G. Chen and K.A. Nelson, “Lifetime of sub-THz coherent acoustic phonons in a GaAs-AlAs superlattice,” Appl. Phys. Lett. 102, 041901 (2013).
  5. N. Boechler, G. Theocharis and C. Daraio, “Bifurcation-based acoustic switching and rectification,” Nature Materials 10, 665, (2011).
  6. N. Boechler, J.K. Eliason, A. Kumar, A.A. Maznev, K.A. Nelson and N. Fang, “Interaction of a contact resonance of microspheres with surface acoustic waves,” Phys. Rev. Lett. 111, 036103 (2013).
  7. N. Boechler, G. Theocharis, S. Job, P.G. Kevrekidis, M.A. Porter and C. Daraio, “Discrete Breathers in One-Dimensional Diatomic Granular Crystals,” Phys. Rev. Lett. 104, 244302 (2010).
  8. G. Theocharis, N. Boechler, P.G. Kevrekidis, S. Job, M.A. Porter and C. Daraio, “Intrinsic energy localization through discrete gap breathers in one-dimensional diatomic granular crystals,” Phys. Rev. E 82, 056604 (2010).
  9. L. Ponson, N. Boechler, Y.M. Lai, M.A. Porter, P.G. Kevrekidis and C. Daraio, “Nonlinear waves in disordered diatomic granular chains,” Phys. Rev. E 82, 021301 (2010).