Abstract
We present a statistical analysis of eigenenergies and discuss several measures of spectral fluctuations and spectral correlations for the van der Waals clusters of different sizes. We show that the clusters become more and more complex with increase in cluster size. We study nearest-neighbor level-spacing distribution , the level number variance , and the Dyson-Mehta statistics for various cluster sizes. For large clusters we find that although the Bohigas-Giannoni-Schmit conjecture seems to be valid, it does not exhibit true signatures of quantum chaos. However, contrasting conjecture of Berry and Tabor is observed with smaller cluster size. For a small number of bosons, we observe the existence of a large number of quasidegenerate states in low-lying excitation which exhibits the Shnirelman peak in distribution. We also find a narrow region of intermediate spectrum which can be described by semi-Poisson statistics whereas the higher levels are regular and exhibit Poisson statistics. These observations are further supported by the analysis of the distribution of the ratio of consecutive level spacings which is independent of unfolding procedure and thereby provides a tool for more transparent comparison with experimental findings than . Thus our detail numerical study clearly shows that the van der Waals clusters become more correlated with the increase in cluster size.
6 More- Received 11 November 2013
DOI:https://doi.org/10.1103/PhysRevA.89.043607
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