Possible evidence for orbital magnetism below the superconducting transition temperature in UBe{sub 12.91}B{sub 0.09}

Although the unconventional nature of the superconductivity in pure and doped UBe{sub 13} has been well established, the precise nature of the superconducting order parameter is still unknown. The authors present muon spin rotation measurements in boron-doped UBe{sub 13} showing a paramagnetic frequency shift below the superconducting transition temperature which is nearly independent of applied magnetic field (0.01--0.10 T), unlike a conventional Knight shift. No increase in linewidth is observed in zero field. These results are compared to observations of the paramagnetic Meissner effect in other superconductors, and are discussed in terms of the possible alignment of orbital moments associated with unconventional superconductivity in this system