Muon spin relaxation and rotation measurements on single crystals of the heavy-fermion superconductor UBe13

We report zero-, longtudinal-, and transverse-field positive muon spin rela xation (mu SR) measurements in single crystals of the heavy-fermion superco nductor UBe13 [T-c=0.83(2) K]. Our zero-field measurements provide an upper limit for any quasistatic magnetic moments in this system below 100 K of 0 .001 mu(B), consistent with previous measurements on polycrystals. From the transverse-field measurements we rind a lower bound for the London penetra tion depth lambda(L) = 1210 nm. This value implies a lower limit for the ef fective mass consistent with the low-temperature specific heat.