Periodic materials can control not only the propagation of light (photonics) but also modify the propagation of elastic (acoustic) waves through the variation of density and elastic constants in space. Phononics define a rich emerging field with unexplored fundamental and applied research through the understanding of the phonon-matter and phonon-photon interactions. In particular, hypersonic (in GHz frequencies) phononics utilize the wealth of soft matter (polymer & colloid science) for the fabrication of mesoscopic structures which can be unique platforms for realization of strong acousto-optic coupling in the visible (phoXonics). In addition, high frequency phonons are the main heat carriers in dielectrics and their propagation through structured materials can be used as a sensitive characterization tool of thermo-mechanical behavior at the nanoscale.
Progress in the field depends on the development of fabrication techniques for patterning at the mesoscale, computation methods of the band structure diagrams and suitable experimental techniques for their record. This necessary integrated approach is being realized in our group utilizing our state of art spontaneous Brillouin Light Scattering (BLS) spectroscopy, design of the structured materials in close collaboration with experimental and theoretical groups in Europe and USA.
Selected current research activities: (i) realization of hypersonic phononic band gaps of different physical origin and generation of localized modes with well-defined polarization and group velocities, (ii) establishment of particle vibration spectroscopy, the colloid equivalent molecular vibration spectroscopy, (iii) search for phoXonic structures with strong “boundary” photoelastic constants to host interaction between fast (THz) light and slow (GHz) phonons, (iv) development of new sensitive techniques for direction dependent thermo-mechanical material behavior.

• Cheng, W.; Wang, J. J.; Jonas, U.; Fytas, G.; Stefanou, N.:
  Observation and tuning of hypersonic bandgaps in colloidal crystals.
  Nature Mater. 5 (10), 2006, 830.
• Still, T., G. Gantzounis, D. Kiefer, G. Hellmann, G. Fytas, N. Stefanou:
  Collective Hypersonic Excitations in Strongly Multiple Scattering Colloids.
  Phys. Rev. Lett. 106 2011, 106.
• Still, T., M. Mattarelli, D. Kiefer, G. Fytas, M. Montagna:
  Eigenvibrations of Submicrometer Colloidal Spheres.
  J. Phys. Chem. Lett. 2010, 2440.
• Guo, Y., A. Morozov, D. Schneider, J. W. Chung, C.Zhang, M. Waldmann, N. Yao, G. Fytas, C. B. Arnold, R. D. Priestley:
  Ultrastable nanostructured polymer glasses.
  Nature Mat. 11 2012, 337-343.