Dynamic reflectionless defects in thight-binding lattices

In tight-binding lattices, localized modes are generally created by the introduction of structural impurities in the otherwise homogeneous lattice. In most cases, impurities are not transparent and cause scattering (reflection) of Bloch wave packets. Here it is shown that the application of high-frequency and strong ac fields in a certain class of lattices with structural impurities can make them reflectionless, yet preserving their localization properties. Hence, a structural defect in the lattice supporting a localized mode, which is a scattering center when the external ac field is switched off, can be dynamically transformed into a reflectionless defect when the external field is switched on.