Role of a nontrivial quantum phase in the dynamical band gap collapse

Abstract

In the quasi-one-dimensional lattice system with a band gap, the effective magnitude of the gap may be reduced, and even collapsed, by applying a monochromatic oscillating external field. The internal relationship between this dynamical band gap collapse (BGC) and the well-known coherent destruction of tunneling (CDT) in the periodically driven two-state model is clarified from a unified point of view. The destructive interference between the resonant scattering paths plays an essential role in both the dynamical BGC and the CDT. This leads to the suppression of the Bragg reflection in the momentum space for the dynamical BGC, and to the suppression of tunneling in the coordinate space for the CDT.