Flatband solitons in the nonlinear media with parity-time symmetric sawtooth lattices

This paper demonstrates solitons in the nonlinear media with parity-time (PT) symmetric sawtooth lattices. These PT lattices exhibit several uncommon features, of which the most striking are the flat Bloch bands, in which the local modes are stable and the depths of imaginary parts are large when the PT symmetry breaks up. Furthermore, we investigate the formation, properties, and dynamics of fundamental, multipole, and two kinds of vortex-carrying solitons that all reside in the semi-infinite bandgaps of the underlying linear Bloch wave spectrum. The stability of these localized gap modes is inspected by direct dynamical simulations of the perturbed solitons, and the results reveal that the lattice parameters significantly influence their stability. Our findings provide valuable insights into soliton physics within the versatile platform of PT-symmetric systems.