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
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
- 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.