The spectral fluctuations and transition intensity fluctuations in the excited-state quantum phase transitions (ESQPTs) have been investigated within the framework of the interacting boson model (IBM) by adopting three statistical measures, including the nearest neighbor level spacing distribution P(S) measuring the chaoticity (regularity) in energy spectra, the Δ3(L) statistics of Dyson and Mehta measuring the spectral rigidity and the intensity distribution P(y) measuring the chaoticity (regularity) in B(E0) transitions. The results indicate that that the ESQPT as a function of the excitation energy may occur as a transition from regular (or semiregular) to highly chaotic if only the associated whole spectrum is chaotic, which fits most of the deformed situations in the IBM including those in the U(5)–SU(3) and SU(3)–O(6) transitional regions. Otherwise, the ESQPT will appear as a transition from regular (or semiregular) to regular such as the cases in the U(5)–O(6) transitional region or those on the ‘Alhassid–Whelan arc’, which represents a nearly regular parameter region connecting the U(5) and SU(3) limits in the IBM.

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We study quantum phase transition of the [Formula: see text] spin model with Dzyaloshinsky–Moriya interaction, by using quantum correlation measures, i.e. quantum deficit and measurement-induced disturbance. It is shown that as the Dzyaloshinsky–Moriya coupling parameter [Formula: see text] increases, the behaviors of quantum phase transition can be suppressed. We also investigate quantum phase transition for the Ising and [Formula: see text] spin models at finite temperature. It is found that quantum phase transition characterized by measurement-induced disturbance is greater than or equal to that characterized by quantum deficit. Other interesting analytical results and numerical results on quantum phase transition for the proposed spin models are also presented by applying the two measures. Furthermore, we also compare quantum deficit and measurement-induced disturbance with quantum entanglement, quantum discord and quantum coherence.

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