Quasiparticle spectrum of the cuprate Bi2Sr2CaCu2O8+δ:: Possible connection to the phase diagram

We previously introduced [T. Cren , Europhys. Lett. 52, 203 (2000)] an energy-dependant gap function, Delta(E), that fits the unusual shape of the quasiparticle (QP) spectrum for both BiSrCaCuO and YBaCuO. A simple anti-resonance in Delta(E) accounts for the pronounced QP peaks in the density of states, at an energy Delta(p), and the dip feature at a higher energy, E-dip. Here we go a step further, our gap function is consistent with the (T,p) phase diagram, where p is the carrier density. For large QP energies (E >Delta(p)), the total spectral gap is Delta(E)similar or equal to Delta(p)+Delta(phi), where Delta(phi) is tied to the condensation energy. From the available data, a simple p dependance of Delta(p) and Delta(phi) is found, in particular, Delta(phi)(p)similar or equal to 2.3k(B)T(c)(p). These two distinct energy scales of the superconducting state are interpreted by comparing to the normal and pseudogap states. The various forms of the QP density of states, as well as the spectral function A(k,E), are discussed.