Accurate theoretical fits to laser-excited photoemission spectra in the normal phase of high-temperature superconductors

It has long been believed that the ‘normal’ (non-superconducting) state of the high-transition-temperature superconductors is anything but normal1,2,3. In particular, this state, which exists above the superconducting transition temperature Tc, has very unusual transport properties4,5 and electron spectral functions6,7, presenting a more difficult, complex and important problem than the superconductivity itself. The origin of this difficulty and complexity resides in the strong electronic correlations, or the many-body Coulomb interactions between electrons, which cannot be properly treated within the standard theories of the electronic structure of solids. A new treatment of these interactions, on the basis of a Gutzwiller projection—which gives zero quasiparticle weight at the Fermi surface and removes the possibility for double electron occupancy on any one site—has recently been proposed8, but fits to available data were unsatisfactory. Here, we compare the electron spectral functions computed within this theoretical treatment with bulk-sensitive measurements made by low-energy photons, using laser-excited angle-resolved photoemission spectroscopy of the superconductor Bi2Sr2CaCu2O8+δ (refs 9, 10). The theory captures the asymmetrical shape of the experimental curves with good accuracy and in principle has only one free parameter. Moreover, no background subtraction is necessary.