Theory of the Normal State of Cuprate Superconductors
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THEORY OF THE NORMAL STATE OF CUPRATE SUPERCONDUCTORS
PHILIP W. ANDERSON and YONG REN, Dept. of Physics, Princeton University, Princeton, N.J. 08544
ABSTRACT We propose a framework for the theory of the "normal" metallic state of the Cu02 planes of high T, superconductors. This state is closely analogous to the known state of the one-dimensional Hubbard model, with spin excitations which can be thought of as chargeless (Z = 0) Fermions occupying the interior of the conventional Fermi surface, and charged excitations which have zero energy near the spanning vectors 2kF of that Fermi surface. The electron spectrum is the composite spectrum of two of these excitations, and can be fitted to angle-resolved photoemission data. When we do so we can calculate or estimate many properties of the normal state in excellent agreement with experiment, and show that the pair susceptibility is anomalously large and temperature-dependent, explaining the high T, and the specific heat behavior.
It is a pleasure to be here to announce that, three years after the MRS meeting here in Boston, at which the phenomenon of high-temperature superconductivity was first confirmed, an underlying theory of this phenomenon can be described with reasonable certainty. Until now we have had only qualitative, descriptive arguments which predict little but make the existence of various observations a little less puzzling; but at this point we are entering the era of quantitative predictions, at least of functional forms, with which experimentalists can compare their data. I have maintained that the core question is the nature of the "normal" metal in the doped CuO2 layers of these superconductors. Much experimental evidence indicates that this is a purely two-dimensional, highly correlated state, whose transport properties and tunneling, infrared and Raman spectrum require a state which is not a conventional Fermi liquid, in that it exhibits some form of separation of charge and spin excitations. Two or three major developments of the past few months have allowed us considerable insight into the nature of this state. Most important is the use of highresolution angle-resolved photoemission spectroscopy, with which one can measure the actual single-particle density of states
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Mat. Res. Soc. Symp. Proc. Vol. 169. c 1990 Materials Research Society
(1) A sample of such
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Ef BINDING ENERGY (eV) Fig. 1 Angle-resolved photoemission data at a series of angles near the supposed Fermi surface, extending to near the center of this zone. The se,:ond panel shows the
bottom four curves superimposed to show the common background and increasing total strength. (Courtesy of C.G. Olson)
It is striking that the resolution is much sharper than the width of the spectrum, so sharp that it i
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