High-temperature superconductors: Occupied and unoccupied electronic states

Abstract
The energy distributions of the occupied and unoccupied electronic states of the high temperature superconductors La1.85Sr0.15CuO4 and YBa2Cu3O6.9 have been identified using x‐ray photoemission, high resolution synchrotron radiation photoemission, inverse photoemission, high resolution synchrotron radiation photoemission, inverse photemission and bremsstrahlung isochromat spectroscopy. These results show low state density from ∼0.5 eV below to ∼3.5 eV above the Fermi energy, EF, well‐defined Cu‐O occupied levels extending to ∼7 eV, the occupied core levels, and the empty Ba, Y, and La states above EF. Copper is shown to be in a nominally 2+ valence state. Comparisons are made with band structure calculations.

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