Discrete Breathers in Nonlinear Lattices: Experimental Detection in a Josephson Array

We present the experimental detection of discrete breathers in an underdamped Josephson-junction array. Breathers exist under a range of dc current biases and temperatures, and are detected by measuring dc voltages. We find that the maximum allowable bias current for the breather is proportional to the array depinning current, while the minimum current seems to be related to a junction retrapping mechanism. We have observed that this latter instability leads to the formation of multisite breather states in the array. We have also studied the domain of existence of the breather at different values of the array parameters by varying the temperature.