In conventional BCS superconductors, the electronic kinetic energy increases upon superfluid condensation (the change ΔEkin is positive). Here we show that in the high critical temperature superconductor Bi2Sr2CaCu2O8+δ, ΔEkin crosses over from a fully compatible conventional BCS behavior (ΔEkin>0) to an unconventional behavior (ΔEkin<0) as the free carrier density decreases. If a single mechanism is responsible for superconductivity across the whole phase diagram of high critical temperature superconductors, this mechanism should allow for a smooth transition between two such regimes around optimal doping.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 1 Sep 2005|