Electronic structure of superconducting UBe13

We have studied the actinide superconductor UBe13 with resonant photoemission using synchrotron radiation 30<~h <~120 eV. In agreement with the anomalously high value of 1.1 J/mole K2, we find a high density of 5f states at the Fermi level EF. Uranium 6d electrons are not present at EF as can be derived from the zero intensity at EF in the off-resonance spectrum. The close resemblance of this off-resonance curve to a photoemission spectrum of pure Be suggests that the hybridization of U 5f electrons with Be s,p electrons is small. Indeed, the UBe13 photoemission curves look like a superposition of U and Be curves. By using photoemission results from UO2 as a reference, we find that the valence-band emission contains about one 5f electron. The present results on UBe13 are compared with those of CeCu2Si2, another member of the family of exotic superconductors. © 1984 The American Physical Society.