Quasiparticle spectrum of the cuprate BiSrCaCuO: Possible connection to the phase diagram

TL;DR

This paper models the quasiparticle spectrum of BiSrCaCuO using an energy-dependent gap function that aligns with the phase diagram, revealing two key energy scales linked to superconductivity and pseudogap states.

Contribution

It introduces a gap function consistent with the phase diagram, connecting quasiparticle spectra with the pseudogap and superconducting states in cuprates.

Findings

The spectral gap at high energies is approximately the sum of two distinct energy scales.

The energy scale related to the condensate is proportional to the critical temperature.

The model explains various features of the quasiparticle density of states.

Abstract

We previously introduced [T. Cren et al., 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 $\Delta(E) \simeq \Delta_p + \Delta_\phi$, 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 $\Delta_\phi(p) \simeq 2.3 k_B T_c(p)$. These two distinct energy scales of the superconducting state are interpreted by comparing with 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.