EVIDENCE FOR POSSIBLE SPIN OR ORBITAL MAGNETISM IN THE SUPERCONDUCTING STATE OF UBE12.91B0.09

Although the unconventional character of the superconductivity in pure and doped UBe13 has been well established, the precise nature of the superconducting order parameter is still unknown. We present muon spin rotation measurements in boron-doped UBe13 showing a paramagnetic fre quency shift below the superconducting transition temperature which is nearly independent of applied magnetic field (0.01-0.10T), unlike a c onventional Knight shift. No increase in line width is observed in zer o field. These results are compared to observations of the paramagneti c Meissner effect in other superconductors, and are discussed in terms of the possible alignment of spin or orbital moments associated with unconventional superconductivity in this system.