Simultaneous occurrence of structure-directed and particle-resonance-induced phononic gaps in colloidal films.
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.
Max Planck Institute for Polymer Research, Mainz, Germany.
T
T
Still
W
W
Cheng
M
M
Retsch
R
R
Sainidou
J
J
Wang
U
U
Jonas
N
N
Stefanou
G
G
Fytas