In this paper we are concerned with the existence of ground states solutions for the following fractional Hamiltonian systems $$ \left\{ \begin{array}{ll} -_tD^α_\infty(_{-\infty}D^α_t u(t)) - λL(t)u(t)+\nabla W(t,u(t))=0,\\[0.1cm] u \in H^α(\mathbb{R},\mathbb{R}^n), \end{array} \right.\qquad(\hbox{FHS})_λ$$ where $α\in (1/2,1)$, $t\in \mathbb{R}$, $u\in \mathbb{R}^n$, $λ>0$ is a parameter, $L\in C(\mathbb{R},\mathbb{R}^{n^2})$ is a symmetric matrix for all $t\in \mathbb{R}$, $W\in C^1(\mathbb{R} \times \mathbb{R}^n,\mathbb{R})$ and $\nabla W(t,u)$ is the gradient of $W(t,u)$ at $u$. Assuming that $L(t)$ is a positive semi-definite symmetric matrix for all $t\in \mathbb{R}$, that is, $L(t)\equiv 0$ is allowed to occur in some finite interval $T$ of $\mathbb{R}$, $W(t,u)$ satisfies Ambrosetti-Rabinowitz condition and some other reasonable hypotheses, we show that (FHS)$_λ$ has a ground sate solution which vanishes on $\mathbb{R}\setminus T$ as $λ\to \infty$, and converges to $u\in H^α(\mathbb{R}, \mathbb{R}^n)$, where $u\in E_{0}^α$ is a ground state solution of the Dirichlet BVP for fractional systems on the finite interval $T$. Recent results are generalized and significantly improved.