  We present a theoretical study of inhomogeneous dynamic (resistive) states in
a single plaquette consisting of three Josephson junctions. These breather
states are found to exist in a large range of control parameters (dc bias,
anisotropy and self inductance). We perform an analytical analysis of these
states, and their stability and resonance behaviour. Numerical calculations
confirm our results and show that instabilities arise due to resonant
interactions between the breather and electromagnetic oscillations mediated by
the breather state. These instabilities manifest themselves by various
nonlinearities, resonant steps and voltage jumps in the current-voltage
characteristics.
