“Dark matter” in crystals: Objects invisible in low-energy electron scattering

The possibility of existing lengthy objects that fundamentally cannot be observed in low-energy electron scattering has been demonstrated. It has been shown in the one-dimensional strong coupling model that a pair of defects can be constructed so that the electron transmission coefficient in the low-energy limit (in the framework of the applicability of the effective mass method) is equal to one. In this limit, these objects are described not as a certain reflectionless potential, but as a homogeneous medium, where the effective size of an object vanishes; i.e., its collapse occurs.