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1994
Chow, KH, Kiefl RF, Schneider JW, Estle TL, Hitti B, Johnston TMS, Lichti RL, Macfarlane WA.  1994.  µSR studies in heavily doped GaAs. Hyperfine Interactions. 86:645-651.   10.1007/bf02068959   AbstractWebsite

Transverse-field (TF) and longitudinal-field (LF) mu+SR measurements have been made on conducting GaAs:Si (n-type almost-equal-to 10(18) cm-3) and GaAs:Zn (p-type almost-equal-to 10(19) cm-3) from 20 mK to 200 K. At low temperatures in GaAs:Si, the frequency spectra show a large diamagnetic signal as well as broad lines due to bond-centered muonium (Mu(BC)). This broadening is attributed to spin exchange interactions with charge carriers in impurity bands. Only the diamagnetic signal is observed in GaAs:Zn. The field dependence of the TF diamagnetic relaxation rate at 5 K can be explained by the combined electric quadrupolar and Zeeman interaction between the muon and the surrounding nuclei and the temperature scan at TF=1.5 T indicates that the mechanisms responsible for the broadening are temperature independent. The candidates for the diamagnetic species are discussed in view of these results.

Mendels, P, Brewer JH, Alloul H, Ansaldo EJ, Noakes DR, Niedermayer C, Collin G, Marucco JF, Stronach CE, Morris GD, Duty TL, Johnston S.  1994.  μSR Study of Zn-Substituted YBa2Cu3Ox. Hyperfine Interactions. 86:577-583.   10.1007/bf02068950   AbstractWebsite

We report zero field and transverse field muSR measurements in magnetic YBa2(Cu1-yZny)3Ox. Mild disorder of the antiferromagnetic state (x < 6.1), a new disordered magnetic phase above x = 6.4 where superconductivity is destroyed by Zn substitution and, finally, local moments iii the paramagnetic state are the most salient features related to Zn substitution described here.

1993
Kiefl, RF, Macfarlane WA, Chow KH, Dunsiger S, Duty TL, Johnston TMS, Schneider JW, Sonier J, Brard L, Strongin RM, Fischer JE, Smith AB.  1993.  Coherence peak and superconducting energy-gap in Rb3C60 observed by muon spin relaxation. Physical Review Letters. 70:3987-3990.   10.1103/PhysRevLett.70.3987   AbstractWebsite

Muon spin relaxation resulting from spin exchange scattering of endohedral muonium (mu+ e-) with thermal electronic excitations has been observed in the fullerene superconductor Rb3C60. The temperature dependence of T1(-1) shows a coherence peak just below T(c) and can be fit to the conventional Hebel-Slichter theory for spin relaxation in a superconductor with a broadened BCS density of states. The average energy gap for electronic excitations, DELTA/k(B)=53(4) K or 2DELTA/k(B)T(c)=3.6(3), is consistent with the BCS weak-coupling limit.

Schneider, JW, Kiefl RF, Chow KH, Johnston S, Sonier J, Estle TL, Hitti B, Lichti RL, Connell SH, Sellschop JPF, Smallman CG, Anthony TR, Banholzer WF.  1993.  Bond-centered muonium in diamond: Resolved nuclear hyperfine structure. Physical Review Letters. 71:557-560.   10.1103/PhysRevLett.71.557   AbstractWebsite

The nuclear hyperfine structure of bond-centered muonium in C-13 enriched diamond has been resolved using time-differential transverse-field muon spin rotation. The measured nearest-neighbor C-13 hyperfine parameters are compared to theoretical values from a recent ab initio Hartree-Fock type cluster calculation. The ratios of the measured C-13 hyperfine parameters and free atom values indicate that 92% of the unpaired electron spin density resides on the two nearest-neighbor atoms, in marked contrast with the situation for the analogous muonium center in Si.