Dynamic localization and quasi-Bloch oscillations in general periodic ac-dc electric fields

We examine the conditions for dynamic localization in general applied periodic ac-dc electric fields. We find that in the presence of both ac and dc components to the field, in addition to traditional dynamic localization, a different type of dynamic localization can occur irrespective of the shape and amplitude of the ac part of the field. These "quasi-Bloch oscillations" take place if the ratio of the Bloch frequency to the ac frequency is a noninteger rational number. Quasi-Bloch oscillations occur only within the tight-binding approximation, but are not restricted to the nearest-neighbor tight-binding limit. This type of dynamic localization provides a more experimentally accessible way to observe dynamic localization in an electronic system than conventional dynamic localization.