Multiplicity for a 4-sublinear Schrödinger-Poisson system with sign-changing potential via Morse theory

In this paper, we study a 4-sublinear Schrödinger-Poisson system with sign-changing potential. Under some suitable assumptions, the existence of two nontrivial solutions are obtained by using the Morse theory. Our result improves the recent ones of Chen and Zhang (2014) [6].