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

Abstract

We previously introduced [T. Cren et al., Europhys. Lett. 52, 203 (2000)] an energy-dependant gap function, Δ(E), that fits the unusual shape of the quasiparticle (QP) spectrum for both BiSrCaCuO and YBaCuO. A simple anti-resonance in Δ(E) accounts for the pronounced QP peaks in the density of states, at an energy Δp, and the dip feature at a higher energy, Edip. 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⪢Δp), the total spectral gap is Δ(E)≃Δp+Δφ, where Δφ is tied to the condensation energy. From the available data, a simple p dependance of Δp and Δφ is found, in particular, Δφ(p)≃2.3kBTc(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.

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