Combining (1) the universal correlations between $T_{ c}$ and $n_{ s}/m^{ *}$ (superconducting carrier density / effective mass) and (2) the pseudo-gap behavior in the underdoped region, we obtain a picture to describe superconductivity in cuprate systems in evolution from Bose-Einstein to BCS condensation. Overdoped and Zn-substituted cuprate systems show signatures of reduced superfluid density in a microscopic phase separation. Scaling of $T_{ c}$ to the superfluid volume density $n_{ s}$ in all these cases indicate importance of Bose condensation.
Categories: cond-mat.supr-con cond-mat.str-el