UNIVERSALITY OF ZERO-DISPERSION PEAKS IN THE FLUCTUATION SPECTRA OF UNDERDAMPED NONLINEAR OSCILLATORS

Zero-dispersion peaks (ZDP's), which can arise in the fluctuation spec tra of noise-driven under-damped oscillators for which the dependence of the eigenfrequency omega(E) on energy E possesses a maximum or mini mum, have been investigated by means of analog electronic experiments. Two different model systems were studied: a tilted Duffing oscillator and a model of a bistable superconducting quantum-interference device (SQUID). It is demonstrated experimentally that, for strong enough in tensity T of Gaussian pseudowhite noise (equivalent to temperature in a thermal system), the shape of a ZDP becomes universal, independent o f the system under investigation. Its evolution with T is also shown t o exhibit universal features, being governed by a single parameter pro vided that T exceeds a critical value T(c), below which the ZDP disapp ears abruptly. The hierarchy of universalities connected to particular types of extrema in omega(E) is discussed. The results are of relevan ce to underdamped SQUID's and, in particular, to the recently discover ed phenomenon of zero-dispersion stochastic resonance.