Soliton propagation in negative-index materials with self-steepening effectShally Loomba, Murugan Senthil Mani Rajan, Rama Gupta and Arumugam MahalingamEur. Phys. J. D, 68 5 (2014) 130DOI: https://doi.org/10.1140/epjd/e2014-40593-9