Soliton propagation in negative-index materials with self-steepening effect Shally Loomba, Murugan Senthil Mani Rajan, Rama Gupta and Arumugam Mahalingam Eur. Phys. J. D, 68 5 (2014) 130 Published online: 22 May 2014 DOI: 10.1140/epjd/e2014-40593-9