  We construct a holographic superconductor model, based on a gravity theory,
which exhibits novel metal-insulator transitions. We investigate the condition
for the condensation of the scalar field over the parameter space, and then
focus on the superconductivity over the insulating phase with a hard gap, which
is supposed to be Mott-like. It turns out that the formation of the hard gap in
the insulating phase benefits the superconductivity. This phenomenon is
analogous to the fact that the pseudogap phase can promote the pre-pairing of
electrons in high $T_c$ cuprates. We expect that this work can shed light on
understanding the mechanism of high Tc superconductivity from the holographic
side.
