Energy band structure of E versus time t for (a) V₀ = 20E_R and (b) V₀ = 30E_R. The amplitude of the SAW is fixed as V_SAW = 30E_R and q = 2. Panel (b) shows that a band crossing occurs between the 2nd and 3rd bands as V₀ increases. Panels (c) and (d) are the topographical maps of the Berry curvature distributions for the 3rd and 4th bands at V₀ = 20E_R. The integrations over the BZ give rise to the Chern number of 0 and 1, respectively.