Unidirectional flow of symbiotic solitons and nonlinear modes of the Schrödinger equation with an external potentialA. Javed, H. Susanto, R. Kusdiantara and I. KourakisEur. Phys. J. Plus, 137 10 (2022) 1146DOI: https://doi.org/10.1140/epjp/s13360-022-03350-x