The Electronic Structure of High Tc Copper-Oxide Superconductors from Photoemission Spectroscopy

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Abstract
This article will summarize the information gained from photoemission spectroscopy (PES) studies of the electronic structure of high temperature superconductor (HTSC) materials, with emphasis on distinguishing models for the normal state. Inverse photoemission spectroscopy (IPES) is a closely related measurement, and taken together PES and IPES yield the single-particle electronic structure, meaning the the spectrum to remove and add electrons, i.e., the electronic ionization and affinity spectrum. It is assumed that the sudden approximation holds, so that the photon event can be characterized by a photoemission cross section σ. The emission from a particular kind of electronic state i can often be identified because its cross section has a particular photon energy (hv) dependence σ (hv).We will emphasize a few recent results especially pertinent to the conceptual issues posed by these materials, and we will divide the discussion between angle-integrated spectra and angle-resolved spectra. For angle-integrated spectra, electrons are collected from the sample surface in a large solid angle, while for angle-resolved spectra, electrons are collected in a well-defined direction. Angle resolution can be used to select emitted electrons of a particular value of crystal momentum k.