Fig. 4: The 2D Bandgap spectra.
From: One- and two-dimensional solitons under the action of the inverted cubic-quintic nonlinearity
a, b The bandgap spectrum produced by the linear version of the 2D equation (5) with potential (2), for V0 = 1 (a) and V0 = 6 (b). The spectrum shows the propagation constant b of Bloch modes vs. the components kx and ky of their quasi-momentum. As in Fig. 1, acronyms SIBG and 1stBG stand for the semi-infinite and the first bandgaps, respectively. In (a), surfaces denote, from top tp bottom, the first, second, third, fourth, and fifth Bloch bands.
