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

Zero-dispersion peaks (ZDP's), which can arise in the fluctuation spectra of noise-driven under-damped oscillators for which the dependence of the eigenfrequency omega(E) on energy E possesses a maximum or minimum, 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 intensity T of Gaussian pseudowhite noise (equivalent to temperature in a thermal system), the shape of a ZDP becomes universal, independent of the system under investigation. Its evolution with T is also shown to exhibit universal features, being governed by a single parameter provided that T exceeds a critical value T(c), below which the ZDP disappears abruptly. The hierarchy of universalities connected to particular types of extrema in omega(E) is discussed. The results are of relevance to underdamped SQUID's and, in particular, to the recently discovered phenomenon of zero-dispersion stochastic resonance.