Cross-Kerr nonlinearity in the surface plasmon polariton waves generated at the interface of graphene and gain mediumHabibur Rahman, Haseena Bibi, M. S. Abdul Jabar and Iftikhar AhmadEPL, 122 5 (2018) 57003DOI: https://doi.org/10.1209/0295-5075/122/57003