Bragg gap solitons in PTPT symmetric lattices with competing nonlinearity

The effect of competing nonlinearity on beam dynamics in parity-time (PTPT) symmetric potentials is investigated. By using numerical methods, the existence of gap solitons is demonstrated in the first Bragg band gap of optical (PTPT) symmetric lattices with competing nonlinearity. Meanwhile, the stability of such solitons is analyzed through introducing a small perturbation to the solitary solutions. The abrupt annihilation of the solitons during propagation demonstrates that the Bragg gap solitons in PTPT symmetric potentials are not stable. In comparison with the on-site gap solitons, the off-site gap solitons exhibit more robust properties during propagation.