Mode Coupling of phonons in a Dense One-Dimensional Microfluidic Crystal

Microfluidic crystals are highly ordered arrangements of water-in-oil droplets flowing in microchannels. Their collective dynamics can exhibit a rich behaviour due to the long-range hydrodynamic interactions mediated by the surrounding phase. In this work, we report the specific excitation of long-lived phonon modes in a dense microfluidic crystal. The excited vibrations show transverse modes that originate from the dipolar flow field around the droplet, whereas the longitudinal modes arise from a non-linear coupling due to the breaking of translational invariance under confinement.