[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

No abstract available

[en] We studied the nonlinear dc conductivity of the slightly hole-doped spin-ladder compounds, Sr_14-xCa_xCu₂₄O₄₁ (x=0 and 1), as a function of electric field. In both the ladder (c-axis) and the rung (a-axis) directions, we observed a definite nonlinear conduction (NLC) below 160 K, although the nature of NLC was quite different between both directions. Detailed studies suggest that only the c-axis NLC for the x=0 material was attributed to the sliding motion of the charge ordered state, which was already suggested by the observation of the sharp resonance in the microwave region. We also suggest that the sliding motion was strongly one-dimensional and easily destroyed by the carrier doping on the ladder, which may be characteristic of this new collective mode in strongly correlated systems

[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] Muon spin relaxation was measured on Rb₂Co_cMg_1-cF₄ to study magnetic ordering and spin fluctuations in diluted Ising spin nets with concentration near the percolation threshold, c_p=0.593. In a c=0.6 compound, the μSR spectrum shows a distinct anomaly due to the long-range ordering of the fractal lattice at 31 K much higher than T_N=20 K. Comparing with the results for a c=0.5 compound, the observed spectra for the c=0.6 compound are analysed in terms of the spin fluctuations of the fractal lattice and the isolated spin clusters which are frozen gradually below 15 K

No abstract available

[en] We have performed detailed measurements to characterize the superconducting (T_c∼1.1 K) state of (TMTSF)₂ClO₄ using both normal and deuterated samples. Using ZF-μSR measurements to search for spontaneous magnetic fields below T_c, we see no evidence for such fields within our resolution, thus we conclude the time reversal symmetry is likely not broken. We have also performed precession measurements in the vortex state of (TMTSF)₂ClO₄. The superconducting relaxation rate decreases strongly with increasing field, which may indicate a dimensional crossover in the nature of the vortex lattice. We estimate that the penetration depth is roughly 535 nm

[en] We have developed a general purpose μSR spectrometer ARTEMIS and installed at S1 experimental area of MLF, J-PARC. The new spectrometer has the identical design with the D1-spectrometer developed in 2013; the common design of the two general purposes spectrometers helps sharing the sample environment apparatus and direct comparison of the beam characteristics between the two experimental areas. We have upgraded the front-end circuit of positron/electron detectors, and achieved high enough hit rate tolerance for muon beam available in the future 1 MW operation of MLF. Other revisions and modifications, which became necessary after the commissioning and the actual usage of the S1/D1 spectrometers have been applied to both of the twin spectrometers. (author)

[en] The spatial field distribution in the flux line lattice state of La_2-xSr_xCuO₄ (LSCO) has been studied by muon spin rotation (μSR). In single-crystalline LSCO samples with x=0.13, 0.15, and 0.19, we have observed large vortex cores at low magnetic induction (≤0.5 T). The possibility of observing a field-induced antiferromagnetic component associated with such large vortex cores is discussed

[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