This section reviews the new direction of research developed from 1994 which is based on the effect of chaotic enhancement of interaction for complex eigenfunctions. This effect was discussed by Sushkov and Flambaum for weak interaction in nuclei (see some details in section 3.6.6). It was shown [69,74,76,80] that the enhancement of interaction can qualitatively change transport properties and destroy Anderson localization. In the phase where all one-particle states are localized the pairs of two repulsive/attractive particles can propagates together on a distance much larger than their size or even be delocalized. This gives the answer to the Bible question "Can two walk together, except they be agreed?" (Amos, (III.3)).
In the metallic phase a critical strength of two-body interaction is defined at which a crossover to quantum chaos and thermalization takes place in Landau Fermi liquid of finite systems [94,96]. These ideas are recently applied to the quantum spin glass shards (clusters).