Steady-state multiple dark photovoltaic spatial solitons Y.H. Zhang, K.Q. Lu, J.B. Guo, K.H. Li and B.Y. Liu Eur. Phys. J. D, 66 3 (2012) 65 Published online: 15 March 2012 DOI: 10.1140/epjd/e2012-20560-4