Signature of superconductivity in UBe13 as seen by neutron scattering: Superconducting and magnetic energy scales

We here present inelastic neutron scattering results on the strongly correlated cubic superconductor UBe13 (T-c = 0.85 K) obtained on a large single crystal by high-resolution cold neutron three-axis spectroscopy. We observed spin dynamics at a unique momentum space position building up below T similar to 50 K and changing significantly on entering the superconducting state. The observed short-range longitudinal character of the correlations can be understood as a result of competing magnetic interactions. The energy dependence in the normal state reflects the energy scales determined from specific heat, whereas the low-temperature data suggest the opening of a superconducting gap. Our findings are consistent with a superconducting order parameter exhibiting s +/- or d-wave symmetry and placing pure UBe13 in the strong coupling regime.