  In this paper we investigate the existence of nontrivial ground state
solutions for the following fractional scalar field equation \begin{align*}
(-\Delta)^{s} u+V(x)u= f(u) \mbox{ in } \mathbb{R}^{N}, \end{align*} where
$s\in (0,1)$, $N> 2s$, $(-\Delta)^{s}$ is the fractional Laplacian, $V:
\mathbb{R}^{N}\rightarrow \mathbb{R}$ is a bounded potential satisfying
suitable assumptions, and $f\in C^{1, \beta}(\mathbb{R}, \mathbb{R})$ has
critical growth. We first analyze the case $V$ constant, and then we develop a
Jeanjean-Tanaka argument \cite{JT} to deal with the non autonomous case. As far
as we know, all results presented here are new.
