Raman-Scattering Measurements and Theory of the Energy-Momentum Spectrum for Underdoped Bi_2Sr_2CaCuO_(8+σ) Superconductors: Evidence of an s-Wave Structure for the Pseudogap

摘要

We reveal the full energy-momentum structure of the pseudogap of underdoped high-T_c cuprate superconductors. Our combined theoretical and experimental analysis explains the spectral-weight suppression observed in the B_(2g) Raman response at finite energies in terms of a pseudogap appearing in the single-electron excitation spectra above the Fermi level in the nodal direction of momentum space. This result suggests an s-wave pseudogap (which never closes in the energy-momentum space), distinct from the d-wave superconducting gap. Recent tunneling and photoemission experiments on underdoped cuprates also find a natural explanation within the s-wave pseudogap scenario.