[en] Magnetic field dependence has been investigated in the c-axis optical conductivity of underdoped YBa₂Cu₃O_6.6. Under the parallel field (H parallel CuO₂ plane), an enhancement of the spectral weight was observed for the 400 cm^-1 peak, in correspondence with the reduction of the superconducting condensate weight. This supports the superconducting origin of this mode, known as the 2nd Josephson plasmon scenario proposed by van der Marel and Tsvetkov. It was also found that parallel field induces a well-defined oscillation mode at the energy scale of the Josephson plasma frequency. Similar phenomena have been observed in a bilayer cuprate Bi₂Sr₂CaCu₂O_8+δ, but not in single layer cuprate La_2-xSr_xCuO₄. Origin of this new mode is discussed

[en] Muon spin relaxation measurements have been performed in the optimally doped La_1.85-yEu_ySr_0.15CuO₄, where the static spin stripes are stabilized by the rare-earth doping. Zero-field measurements indicate that the volume fraction V_Cu of static magnetism increases with increasing Eu concentration, while the ordered moment size remains constant. Transverse-field measurements show that n_s/m^* (superconducting carrier density/effective mass) at T→0 is proportional to the non-magnetic volume fraction (1-V_Cu). These results indicate that superconductivity and static stripe magnetism occur in different spatial regions, exclusively, suggestive of microscopic phase separation

[en] A discontinuous change of muon-spin precession frequencies in CaV₃O₇ is observed at T∼0.2 K, indicating a possible spin reorientation. Our results suggest that CaV₃O₇ possesses the identical spin direction as isostructural SrV₃O₇ below ∼0.2 K, although the spin directions in the two compounds are different at higher temperatures as determined by elastic neutron scattering

[en] Muon spin relaxation measurements have been performed in the two dimensional spin system SrCu₂(BO₃)₂. As the temperature decreases, the relaxation rate increases below T=10 K, and shows a saturation below T=3 K. The line shape at low temperatures is nearly Gaussian, yet it cannot be easily decoupled by an application of longitudinal field. These results indicate the existence of magnetically active spins that show slowing down of fluctuations with decreasing temperatures, yet remain dynamic even at 0.1 K. We have also examined a sample doped with small amount of non-magnetic Zn²⁺ impurity, Sr(Cu_0.99Zn_0.01)₂(BO₃)₂. The result was quite similar to the pure sample. Thus, anomalous behavior of the pure sample observed in low temperatures is not due to magnetic moments induced by impurities or a lattice defect

[en] AgNiO₂, a model compound of an S=1/2 triangular lattice, was studied by muon spin relaxation in addition to ac, dc susceptibility, electrical resistivity and neutron diffraction. The relaxation rate shows a sharp peak at around T_N=28 K followed by a sudden decrease of initial asymmetry indicating a magnetic ordering. Three internal fields ranging from 0.2 to 0.3 T were obtained from the muon precession period. However, a neutron diffraction experiment failed to detect any magnetic order at low temperatures. From these results, it was concluded that magnetic coherence is confined to small domain compared with the coherence length of neutron diffraction due to spin frustration

[en] MgB₂ thin films with T _c = 19 K were fabricated by the ion ablation technique utilizing a high-energy pulsed ion beam. A target remains pure MgB₂ after ablation, proving the excellent capability of ablation by the high-power ion beam. Chemical compositions of the deposited material, however, may vary with positions of the substrates from the beam axis. X-ray diffraction patterns exhibit only (0 0 1) and (0 0 2) peaks, which indicate a c-axis orientation of the films. Scanning electron microscopy images show a possible growth of single crystals with hexagonal shape and 1 μm size

[en] MgB₂ thin films were deposited by the ablation technique utilizing high-energy pulsed ion beam of 700 keV and 10 J/cm² pulse. The target plates are fabricated by sintering MgB₂ stoichiometric powder at 1100 ^oC being encapsulated. The MgB₂ films are preferentially c-axis oriented on r-cut Al₂O₃ substrates, in spite of the high quenching rate. A possible growth of MgB₂ single crystals with hexagonal shape and 1 μm in size is observed on the film surface. Upon conducting post-annealing at 600 ^oC, the films become superconducting with the transition temperature T _c = 11 K

[en] Zero-field (ZF) and transverse-field (TF) μSR measurements have been performed on a superconducting La₂CuO_4+y crystal with y=0.12 where excess oxygen is intercalated to form a stage-4 structure. Measurements are made on the same single-crystal sample studied in the neutron scattering measurements of Lee et al. [Phys. Rev. B 60 (1999) 3643] who find that both superconductivity and static incommensurate magnetic modulation develop below $\text{T}{}_{\mathrm{<mtext>c</mtext>}}\text{∼T}{}_{\mathrm{<mtext>N</mtext>}}\text{∼42}\text{K}$. The amplitude of the muon precession signal observed in ZF-μSR increases progressively below T_N and saturates at T→0 to the value which indicates that a static magnetic field from Cu moments exists in only a part of muon sites corresponding to a magnetic site fraction of V_M=41%. The observed frequency ∼3.5 MHz of the precession signal suggests the development of a large (at least $\text{0.4}\text{μ}{}_{\mathrm{<mtext>B</mtext>}}$) static Cu moment near the “magnetic” muon sites. Comparing the TF-μSR results with computer simulations, we obtained V_M(T→0)=42%.

[en] We present zero-field muon spin relaxation (μSR) measurements of La_1.6-xNd_0.4Sr_xCuO₄ with x=0.125,0.15,0.2;thinspLa_1.475Nd_0.4Ba_0.125CuO₄,La_1.875B

[en] We report elastic neutron diffraction and muon spin relaxation (μSR) measurements of the quasi-one-dimensional antiferromagnets Sr₂CuO₃ and Ca₂CuO₃, which have extraordinarily reduced T_N/J ratios. We observe almost resolution-limited antiferromagnetic Bragg reflections in Sr₂CuO₃ and obtain a reduced ordered moment size of ∼0.06μ_B. We find that the ratio of ordered moment size μ(Ca₂CuO₃)/μ(Sr₂CuO₃)=1.5(1) roughly scales with their Nacute eel temperatures, which suggests that the ordered moment size of quasi-one-dimensional antiferromagnets decreases continuously in the limit of vanishing interchain interactions. copyright 1997 The American Physical Society