Hidden Defect Pairs: Objects Invisible in Low-Energy Electron Scattering
  Objects composed of lattice defects exist within a one-dimensional tight-binding model whose electron reflection coefficient in the low-energy case is equal to zero. Localized states are absent as well. The effective mass concept explains this not as some kind of reflectionless potential but as homogeneous medium, in which effective object size collapses. Without making effective mass approximations a new type of resonance is observed, in which the reflection coefficient becomes zero at a certain energy. 
A.A. Gorbatsevich