In this paper, we consider the following perturbed second-order Hamiltonian system −u¨(t) + L(t)u = ∇W(t, u(t)) + ∇G(t, u(t)), ∀ t ∈ R, where W(t, u) is subquadratic near origin with respect to u; the perturbation term G(t, u) is only locally defined near the origin and may not be even in u. By using the variant Rabinowitz’s perturbation method, we establish a new criterion for guaranteeing that this perturbed second-order Hamiltonian system has infinitely many homoclinic solutions under broken symmetry situations. Our result improves some related results in the literature
