Electronic structure of superconducting UBe13

We have studied the actinide superconductor UBe₁₃ with resonant photoemission using synchrotron radiation 30<=hν<=120 eV. In agreement with the anomalously high γ value of 1.1 J/mole K², we find a high density of 5f states at the Fermi level E_F. Uranium 6d electrons are not present at E_F as can be derived from the zero intensity at E_F 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.