Torus doubling resonances and breather stability.

Discrete breathers that arise in doped alkali halides lead us to study two properties of these localized excitations. First, we note a bifurcation phenomenon, which we dub torus doubling, in which resonant coupling in the nonlinear modes induces a period doubling of the phase space structure. Second, we find that although two-frequency breather excitations are not in principle localized (because of phonon resonances), in practice they can survive 10;{9} times the characteristic time scale and give rise to marked physical phenomena, including the one that brought us to this study, the anomalous decay of luminescence.

Low temperature delayed recombination and trap tunneling.

Delayed recombination of charge carriers at an activator is a significant problem for fast scintillators and is usually associated with thermal effects. However, experimental results have shown that this phenomenon can occur even at the lowest temperatures. We here provide evidence in support of the idea that this is due to quantum tunneling between activator and nearby traps, and provide analytic estimates relating the energy levels and locations of those traps to the observed delayed recombination. Several calculations are devoted to showing that deviations from the simplest estimates in fact do not occur. Moreover, these estimates are consistent with lower dimensional numerical calculations for a physically significant range of trap distances. In two examples involving the activator Pr, the formulas developed are used to give the locations of traps based on likely values of trap energy depth.

Role of breathers in anomalous decay.

We have previously presented evidence for the formation of breathers in doped alkali halides subjected to a flash of UV light. Properties of these breathers, their phase space structure, robustness, decay, and propensity for formation, are studied here. Under a wide range of parameters and interionic potentials they form two-dimensional Kolmogorov-Arnold-Moser tori (less than generic) in phase space. Strobed views of these tori, useful in quantization, are shown. All features support the thesis of breather formation as the explanation for the luminescence decay anomaly that first motivated our breather proposal.

Stability of quantum breathers.

Using two methods we show that a quantized discrete breather in a 1D lattice is stable. One method uses path integrals and compares correlations for a (linear) local mode with those of the quantum breather. The other takes a local mode as the zeroth order system relative to which numerical, cutoff-insensitive diagonalization of the Hamiltonian is performed.

Slow relaxation, confinement, and solitons.

Millisecond crystal relaxation has been used to explain anomalous decay in doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons. Our model exhibits confinement of mechanical energy released by excitation. Extending the model to long times is justified by its relation to solitons, excitations previously proposed to occur in alkali halides. Soliton damping and observation are also discussed.