Evolution of the quasiparticle spectral function in cuprates

We analyzed photoemission data for several doping levels of the Bi2Sr2CaCu2O8+x compounds, ranging from overdoped to underdoped. We show that the high frequency part of the spectra near (0,pi) can be described by Fermi liquid theory in the overdoped regime, but exhibits a non-Fermi liquid behavior in the underdoped regime. We further demonstrate that this behavior fits reasonably well to a 1/(sqrt omega) behavior suggested for systems with strong spin fluctuations.