  The studies of high-quality single-domain crystals of YbB12 were carried out
by the precise x-ray diffraction technique in combination with the low
temperature polarized THz - infrared spectroscopy and accurate magnetotransport
measurements. It has been shown for the first time that this archetypal
strongly correlated system with a metal-insulator transition to a mysterious
dielectric ground state with a metal Fermi surface (Science 362, 65-69 (2018)
and ibid 362, 32-33 (2018)) is actually a heterogeneous compound in the regime
of electronic phase separation. Changes in the configuration of the discovered
dynamic charge stripes are investigated upon cooling, as a result, a conclusion
is drawn in favor of a crossover between different patterns of the filamentary
electronic structure penetrating the semiconducting matrix of YbB12. We argue
that the discovery of stripes in YbB12 is fundamental, elucidating the nature
of exotic dielectric state in Kondo insulators.
