In this paper we are concerned with the existence of infinitely many
homoclinic solutions for the following fractional Hamiltonian systems {-tD??(-?D?tu(t))-L(t)u(t) + ?W(t,u(t)) = 0, u ? H?(R,Rn), (FHS)
where ? ? (1/2,1), t ? R, u ? Rn, L ? C(R,Rn2) is a symmetric matrix for
all t ? R, W ? C1(R x Rn,R) and ?W(t,u) is the gradient of W(t,u) at u.
The novelty of this paper is that, when L(t) is allowed to be indefinite
and W(t,u) satisfies some new superquadratic conditions, we show that (FHS)
possesses infinitely many homoclinic solutions via a variant fountain
theorem. Recent results are generalized and significantly improved.