Spin-Triplet p-Wave Superconductivity Revealed under High Pressure in UBe13

To unravel the nature of the superconducting symmetry of the enigmatic 5f heavy-fermion UBe13, the pressure dependence of the upper critical field and of the normal state are studied up to 10 GPa. Remarkably, the pressure evolution of the anomalous H-c2 (T, P) over the entire pressure range up to 5.9 GPa can be successfully explained by the gradual admixture of a field-pressure-induced E-u component in an A(1u) spin-triplet ground state. This result provides strong evidence for parallel-spin pairing in UBe13, which is also supported by the recently observed fully gapped excitation spectrum at ambient pressure. Moreover, we have also found a novel non-Fermi-liquid behavior of the resistivity, rho(T) similar to T-n (n less than or similar to 1), which disappears with the collapse of the negative magnetoresistance behavior and the existence of a superconducting ground state around P = 6 GPa, suggesting a close interplay between Kondo scattering and superconductivity.