Energy-Dependent Enhancement of the Electron-Coupling Spectrum of the UnderdopedBi2Sr2CaCu2O8+δSuperconductor

Abstract

We have determined the electron-coupling spectrum of superconducting Bi2Sr2CaCu2O(8+δ) from high-resolution angle-resolved photoemission spectra by two deconvolution-free robust methods. As hole concentration decreases, the coupling spectral weight at low energies ≲15 meV shows a twofold and nearly band-independent enhancement, while that around ∼65 meV increases moderately, and that in ≳130 meV decreases leading to a crossover of dominant coupling excitation between them. Our results suggest the competition among multiple screening effects, and provide important clues to the source of sufficiently strong low-energy coupling, λ(LE)≈1, in an underdoped system.