Dynamical self-trapping of two-dimensional binary solitons in cross-combined linear and nonlinear optical lattices
Dynamical and self-trapping properties of two-dimensional (2D) binary mixtures of Bose-Einstein condensates (BECs) in cross-combined lattices consisting of a one-dimensional (1D) linear optical lattice (LOL) in the $x-$ direction for the first component and a 1D non linear optical lattice (NOL) in the $y$-direction for the second component, are analytically and numerically investigated. The existence and stability of 2D binary matter wave solitons in these settings is demonstrated both by variational analysis and by direct numerical integration of the coupled Gross-Pitaevskii equations (GPE). We find that in absence of the NOL binary solitons, stabilised by the action of the 1D LOL and by the attractive inter-component interaction can freely move in the $y-$direction. In the presence of the NOL we find, quite remarkably, the existence of threshold curves in the parameter space separating regions where solitons can move, from regions where the solitons become dynamically self-trapped. The mechanism underlying the dynamical self-trapping phenomenon (DSTP) is qualitatively understood in terms of a dynamical barrier induced by the the NOL similar to the Peirls-Nabarro barrier of solitons in discrete lattices. DSTP is numerically demonstrated for binary solitons that are put in motion both by phase imprinting and by the action of external potentials applied in the $y-$direction. In the latter case we show that the trapping action of the NOL allows maintaining a 2D binary soliton at rest in a non-equilibrium position of a parabolic trap, or to prevent it from falling under the action of gravity. Possible applications of the results are also briefly discussed.