Observations of impurity-soliton interactions in driven Frenkel-Kontorova chains

We have investigated experimentally the interactions between the impurities and envelope solitons in nonlinearly coupled pendulum chains subject to vertical vibrations. The experiments show that a defective pendulum in length will attract or repel the solitons including breather and kink, supplying an evidence to numerical results made recently. The characteristic of the interactions, attraction or repulsion, is not only dependent on the polarity of the impurities, but also on the driving frequency and topology of the solitons. These observations testify to some perfect symmetries between long and short defects, breather and kink solitons in impurity-soliton interactions. The intensity of the interaction is related to the defect intensity and driving amplitude. Numerical simulations have also reproduced all of the observations in the framework of a discrete model.