  We study the Bose--Einstein condensation in a tight-binding model with a
hopping rate enhanced only on a surface. We show that this model exhibits two
different critical phenomena depending on whether the hopping rate on the
surface $t_s$ exceeds the critical value $5t/4$, where $t$ is the hopping rate
in the bulk. For $t_s/t<5/4$, normal Bose--Einstein condensation occurs, while
the Bose--Einstein condensation for $t_s/t\geq5/4$ is characterized by the
spatial localization of the macroscopic number of particles at the surface. By
exactly calculating the surface free energy, we show that for $t_s/t<5/4$, the
singularity of the surface free energy stems from diverging the correlation
length in the bulk, while for $t_s/t\geq5/4$, it is induced by the coupling
effects between the bulk and surface.
