  Based on the Wilson's criterion metal-insulator, extended to materials with
strong electronic correlations, we have identified a specific class of the
materials, which is not associated with their usual classification into
Mott-Hubbard and charge transfer dielectrics. The local symmetry of these
materials leads to a disappearance of quasiparticle states (so-called first
removal or fist extra states) in the Hubbard's gap. It's especially unusual for
the doped materials, where quasiparticles - charge carriers can disappear or
appear under external factors, but the Mott transition has not yet been
achieved. In the work we introduced the so-called a "quasiparticle
transparency", and also provided specific experiments to identify the materials
with the low quasiparticle transparency. Some examples of these materials with
a spin crossover under high pressure and showing Jahn-Teller nature have been
observed.
