Electronic structure of potassium-dopedLa@C82metallofullerene studied with photoelectron spectroscopy

Abstract

The electronic structure of potassium-doped $\mathrm{La}@{\mathrm{C}}_{82}$ has been studied with synchrotron-radiation photoelectron spectroscopy. Ultraviolet photoemission measurements indicate evolution of the valence-band states of $\mathrm{La}@{\mathrm{C}}_{82}$ with increasing potassium content, but ${\mathrm{K}}_{x}\mathrm{La}@{\mathrm{C}}_{82}$ remains semiconducting for all $x$ between 0 and 6, with a band gap of at least $0.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, in contrast to K-doped ${\mathrm{C}}_{60}$. The valence-band features, including those which arise from the interactions of ${\mathrm{C}}_{82}$ cages with La and K, show oscillatory behavior of photoemission intensity with incident photon energy. The strength of the oscillations varies between the states, and we associate diminished oscillations with increased localization of electron density. Finally, although core and valence states of $\mathrm{La}@{\mathrm{C}}_{82}$ change considerably with potassium dosage, the encapsulated La atom is well shielded from the outside chemical environment and its valency remains close to $3+$.