Odd and even subharmonics and chaos in RF SQUIDS

The authors discuss multistable RF SQUIDs under weak damping, driven by an external flux applied at resonance frequency. Rich subharmonic spectra and several bands of chaotic behaviour are found as functions of the amplitude of the drive. In addition to period-doubling Feigenbaum sequences, they also encounter an odd subharmonic route to the phase-unlocked regime. The principal chaotic band displays new intrinsic structure, which arises due to an abrupt symmetry break from an orbit with period-5 character to one resembling a period-2 orbit. However, at higher amplitudes of the drive, the symmetry becomes continuously restored.