Simultaneous occurrence of structure-directed and particle-resonance-induced phononic gaps in colloidal films

Phys Rev Lett. 2008 May 16;100(19):194301. doi: 10.1103/PhysRevLett.100.194301. Epub 2008 May 13.


We report on the observation of two hypersonic phononic gaps of different nature in three-dimensional colloidal films of nanospheres using Brillouin light scattering. One is a Bragg gap occurring at the edge of the first Brillouin zone along a high-symmetry crystal direction. The other is a hybridization gap in crystalline and amorphous films, originating from the interaction of the band of quadrupole particle eigenmodes with the acoustic effective-medium band, and its frequency position compares well with the computed lowest eigenfrequency. Structural disorder eliminates the Bragg gap, while the hybridization gap is robust.