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Electronic states and depolarization phenomena are studied for theμ+ in cis- and transpolyacetylene (CH)x. Formation of weakly bound muonium-like paramagnetic state is found in cis-(CH)x at room temperature, while diamagneticμ+ state is formed in trans-(CH)x. The origin of this clear difference might reflect properties of excitation modes in these two-isomers.

The average polarization Pav of the recoil nucleus12B (ground state) produced by the polarized-muon capture reaction12C(μ−,vμ)12B was measured by a new approach which involved the muon spin resonance, and the adoption of Grafoil as a carbon target where the polarization of12 B can be preserved completely under 3 kG holding field. Our observed resultPav=0.473±0.053 yields gp/gA=9.6−2.72.4 which seems to be consistent with the canonical PCAC prediction within the error.

Abstract: NMR measurements on12B nuclei implanted in a thin sheet of highly oriented pyrolytic graphite (Grafoil) have been made to study the magnitude of the polarization of12B and its electric quadrupole coupling. The magnitude of the residual polarization of12B held in carbon material is of crucial importance to the experiment measuring the average polarization of12B produced in the muon capture by12C. It was found that the polarization of12B can be maintained at 101.02.2% in Grafoil under a magnetic field of 3 kG. The electric quadrupole coupling was determined to bee 2 qQ/h=+1207.38.2 kHz. From the magnitude and the sign of the electric field gradienteq, the location of12B was found to be a substitutional site in the carbon lattice. The anomalous B-C bond involving thesp 2 hybrid orbitals with partially filledp z electrons is also discussed.

Abstract: The negative muon spin rotation method (μ− SR) has been applied to studies of electronic states at oxygen sites of oxide superconductors YBa2Cu3O7, Nd2−x Ce x CuO4−δ (x=0.15, oxygen reduced), LiTi2O4 and related oxide-insulators La2CuO4−δ, CuO, Cu2O. The paramagnetic shifts of μ− trapped at oxygen nuclei in these polycrystalline powder samples have been measured at 300 K. All the measured shifts are positive. In copper-oxides the paramagnetic shifts are of the order 10−3, while in LiTi2O4 is very small (8.43.3410−5). In YBa2Cu3O7, a fast μ− spin relaxation timeT 2* (∼ 200 ns) has been observed; the reason for this is unknown and further studies are now in progress.