Collapse of electron band gaps in periodical structures dressed by a high-frequency field

It is demonstrated theoretically that the strong interaction between electrons in periodical structures and a high-frequency electromagnetic field suppresses the Bragg reflection of the electrons. As a result, the band gaps in electron energy spectra of the structures (the Bragg gaps) are collapsed. This quantum phenomenon can take place in various periodical structures, including both natural crystalline solids and artificial superlattices.