Traits of the insulator formed under the superconductor-insulator transition

Various experimental observations of the magnetic-field-induced superconductor-insulator transition are described and compared with different theoretical models: one based on boson-vortex duality, next exploring the properties of granular superconductors and the third analyzing effect of the superconducting fluctuations in the magnetic field at low temperature. All the models point to the existence of pairwise electron correlations at the Fermi-level of the insulator. These so-called localized pairs should vanish in high magnetic fields. The localized pairs apparently come from the parity effect in ultrasmall quasigrains - local minima of the random potential which can admit only small limited number of electrons