Unoccupied electronic states and surface phenomena for Y<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>6.9</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Inverse photoemission was used to probe the unoccupied electronic levels within 25 eV of ${E}_{F}$ for the high-temperature superconductor Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.9}$. Our results show that the density of states is low from ${E}_{F}$ to \ensuremath{\approx}3.7 eV above ${E}_{F}$. Large emission features appearing at 6.6 and 8.6 eV are associated with Ba $5d$- and Y $4d$-derived bands, respectively, while a structure at 13.4 eV above ${E}_{F}$ is due to localized Ba $4f$ states. Energy-dependent studies reveal a dispersive band between \ensuremath{\approx}4 and \ensuremath{\approx}6 eV above ${E}_{F}$. An oxygen-induced feature was observed at 1.8 eV, but there is no evidence that high-energy electron-stimulated desorption removes these chemisorption states.

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