  Despite its fundamental and practical interest, the understanding of
mesoscopic effects in strongly coupled superconductors is still limited. Here
we address this problem by studying holographic superconductivity in a disk and
a strip of typical size $\ell$. For $\ell < \ell_c$, where $\ell_c$ depends on
the chemical potential and temperature, we have found that the order parameter
vanishes. The superconductor-metal transition at $\ell = \ell_c$ is controlled
by mean-field critical exponents which suggests that quantum and thermal
fluctuations induced by finite size effects are suppressed in holographic
superconductors. Intriguingly, the effective interactions that bind the order
parameter increases as $\ell$ decreases. Most of these results are consistent
with experimental observations in Pb nanograins at low temperature and
qualitatively different from the ones expected in a weakly coupled
superconductor.
