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

Abstract

It has long been believed that the ‘normal’ (non-superconducting) state of the high-transition-temperature superconductors is anything but normal^1,2,3. In particular, this state, which exists above the superconducting transition temperature T_c, has very unusual transport properties^4,5 and electron spectral functions^6,7, 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 Bi₂Sr₂CaCu₂O_8+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.