Superfluid density in cuprate high-Tcsuperconductors: A new paradigm

We show that the Uemura relation, namely T c proportional to superfluid density p s , is not generally satisfied in high-T c superconductors. Instead, a modified plot of T c /Δ 0 versus p s where Δ 0 is the maximum d-wave gap at T=0, exhibits universal features that point to an alternative interpretation of the underlying physics. In the underdoped region this plot exhibits the canonical negative curvature expected when a ground-state correlation competes with superconductivity (SC) by opening up a gap (the pseudogap) in the normal-state density of states. Moreover we observe simple linear relations between T c p s , the electronic entropy at T c , and the critical impurity concentration for suppressing SC. These relations confirm that the pseudogap persists to T = 0, strongly modifying the SC ground state.