THE SUPPRESSION OF A BLOCH BAND IN A DRIVING LASER FIELD

The dynamic effect of Bloch electrons in a spatial periodic system under the influence of a driving laser field is studied within the single-band approximation. A quasienergy band is obtained exactly for the case of long-range intersite interactions. It is found that the quasienergy band will be suppressed heavily by the laser field if the ratio of the Bloch frequency to the laser frequency is a root of the ordinary Bessel function of order zero. If only the nearest-neighbour intersite interaction is involved, the band suppression will tum into the band collapse proposed very recently. However, a numerical calculation of the band width shows that in comparison with the nearest-neighbour intersite interaction, the contribution of other intersite interactions to the quasienergy is not negligible. This may imply that the experimental observation of the dynamic effect will be that of band suppression rather than band collapse.