W. L. Yang,¹³ V. Brouet,³¹⁴ X. J. Zhou,³ Hyoung J. Choi,⁵ Steven G. Louie,²⁵ Marvin L. Cohen,²⁵ S. A. Kellar,³ P. V. Bogdanov,³ A. Lanzara,³ A. Goldoni,⁶ F. Parmigiani,⁷ Z. Hussain,¹ Z.-X. Shen^3*

C₆₀ fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C₆₀ monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.

¹ Advanced Light Source (ALS),
² Materials Science Division, Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA 94720, USA.
³ Department of Physics, Department of Applied Physics, and Stanford Synchrotron Radiation Laboratory (SSRL), Stanford University, Stanford, CA 94305, USA.
⁴ Laboratoire de Physique des Solides, CNRS, UMR8502, Universite Paris-Sud, Bat 510, 91405 Orsay, France.
⁵ Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.
⁶ Sincrotrone Trieste S.C.p.A., S.S. 14 Km 163.5, in Area Science Park, 34012 Trieste, Italy.
⁷ Istituto Nazionale per la Fisica della Materia-Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore, Via dei Musei 41, 25121 Brescia, Italy.
^*   To whom correspondence should be addressed. E-mail: zxshen{at}stanford.edu