We have performed transverse-field muon spin relaxation measurements of the Zn-substituted cuprate high-T c superconductors: La 22x Sr x ͑Cu 12y Zn y ͒O 4 and YBa 2 ͑Cu 12y Zn y ͒ 3 O 6.63 . The superconducting carrier density͞effective mass n s ͞m ‫ء‬ ratio at T ! 0 decreases with increasing Zn concentration, in a manner consistent with our "swiss cheese" model in which charge carriers within an area pj 2 ab around each Zn are excluded from the superfluid. We discuss this result in the context of Bose condensation, pair localization, and pair breaking. [S0031-9007(96)02011-X]

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We have performed muon spin relaxation measurements of the frustrated kagome lattice spin system SrCr8Ga4019. Our results demonstrate the slowing down of the Cr spin fluctuations when cooling toward the susceptibility-cusp temperature Tg 3 5 K The saturation of the relaxation rate below Tg, together with its weak dependence on longitudinal field (LF) between 0 and 2 kG, indicates the presence of dynamic spin fluctuations persisting even at T -100 mK without static order parameter. We propose a spin-liquid type ground state to explain an undecouplable Gaussian shape of the relaxation function observed at T~T , .

We report muon spin rotation-relaxation measurements of the heavy fermion superconductor UPt3. The broadening of the transverse field muon precession signal sets in approximately 60 mK below T c , a temperature which corresponds to the lower superconducting transition. In zero applied magnetic field, we observe an increase in the internal magnetic field within the superconducting state which can be explained if the "lower superconducting phase" in the H-T phase diagram of UPt3 is characterized by broken time-reversal symmetry.

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