Correlation-hole method for the spectra of superconducting microwave billiards

The spectral fluctuation properties of various two- and three-dimensional superconducting billiard systems are investigated by employing the correlation-hole method. It rests on the sensitivity of the spectral Fourier transform to long-range correlations and is thus an alternative technique to study chaotic dynamics. First, we apply the method to the eigenfrequencies that are extracted from the measured resonances. Second, we analyze the unfolded raw spectra, including the shape of the resonances. The merit of the method lies in a clear separation of the statistics due to the positions and due to the shape of the resonances. However, we show that statistical fluctuations of the intensities of the resonances have a strong impact on the observable. Therefore, the visibility of the correlation hole is studied as a function of the number of independent statistical variables entering into the intensities. The visibility improves if independent spectra are superimposed.