Incipience of quantum chaos in the Jahn-Teller model

TL;DR

This paper investigates the spectral properties of the Jahn-Teller model, revealing complex spectral regions, level clustering, and signatures of quantum chaos through statistical analysis of energy levels.

Contribution

It uncovers the coexistence of multiple spectral regions and identifies quantum chaos indicators in the Jahn-Teller model's complex spectra.

Findings

Identification of three spectral regions: dimerized, kink lattice, and kink nucleation.

Observation of level clustering and avoiding levels indicating complex spectral structure.

Linear scaling of level curvature distributions as a signature of quantum chaos.

Abstract

We studied complex spectra of a two-level electron system coupled to two phonon (vibron) modes represented by the E$\otimes$e Jahn-Teller model. For particular rotation quantum numbers we found a coexistence of up to three regions of the spectra, (i) the dimerized region of long-range ordered (extended) pairs of oscillating levels, (ii) the short-range-ordered (localized) "kink lattice" of avoiding levels, and (iii) the intermediate region of kink nucleation with variable range of ordering. This structure appears above a certain critical line as a function of interaction strength. The level clustering and level avoiding generic patterns reflect themselves in several intermittent regions between up to three branches of spectral entropies. Linear scaling behavior of the widths of level curvature probability distributions provides the conventionally adopted indication for the presence of quantum chaos. Level spacing probability distributions show peculiarities of the partial (for fixed quantum angular momentum) as well as of the cumulative (all angular momenta) case. The clustering of levels with two and three dominant spacings at fixed angular momenta causes notable deviations of the cumulative distributions from the Poissonian one.