Electronic structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">x</mml:mi></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">C</mml:mi></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>fullerides

Abstract

Photoemission and inverse photoemission studies of ${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{C}}_{60}$ films show insulating character for x3\ifmmode\pm\else\textpm\fi{}0.3 as states derived primarily from the LUMO orbitals of ${\mathrm{C}}_{60}$ are occupied. Metallic character is observed at higher Ca content as a second band of states is partially occupied. This band has mixed character since it is derived from the LUMO+1 orbitals of ${\mathrm{C}}_{60}$ and the Ca s states. These states are responsible for superconductivity in ${\mathrm{Ca}}_{5}$${\mathrm{C}}_{60}$.