Nontrivial solutions of Schrödinger equations with indefinite nonlinearities

We prove the existence of nontrivial solutions for the Schrödinger equation − u+V (x)u = aγ (x)f (u) in RN, where f is superlinear and subcritical at zero and infinity respectively, V is periodic and a(x) changes sign. © 2007 Elsevier Inc. All rights reserved.