616 research outputs found

    NMR and NQR study of pressure-induced superconductivity and the origin of critical-temperature enhancement in the spin-ladder cuprate Sr2_2Ca12_{12}Cu24_{24}O41_{41}

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    Pressure-induced superconductivity was studied for a spin-ladder cuprate Sr2_2Ca12_{12}Cu24_{24}O41_{41} using nuclear magnetic resonance (NMR) under pressures up to the optimal pressure 3.8 GPa. Pressure application leads to a transitional change from a spin-gapped state to a Fermi-liquid state at temperatures higher than TcT_c. The relaxation rate 1/T11/T_1 shows activated-type behavior at an onset pressure, whereas Korringa-like behavior becomes predominant at the optimal pressure, suggesting that an increase in the density of states (DOS) at the Fermi energy leads to enhancement of TcT_c. Nuclear quadrupole resonance (NQR) spectra suggest that pressure application causes transfer of holes from the chain to the ladder sites. The transfer of holes increases DOS below the optimal pressure. A dome-shaped TcT_c versus pressure curve arises from naive balance between the transfer of holes and broadening of the band width

    The degree of aqueous alteration of nine CM chondrites estimated from mineralogy and chemical variations of matrix.

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    第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日(木) 国立国語研究所 2階講

    Vortex reflection at boundaries of Josephson-junction arrays

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    We study the propagation properties of a single vortex in square Josephson-junction arrays (JJA) with free boundaries and subject to an applied dc current. We model the dynamics of the JJA by the resistively and capacitively shunted junction (RCSJ) equations. For zero Stewart-McCumber parameter βc\beta_c we find that the vortex always escapes from the array when it gets to the boundary. For βc2.5\beta_c\geq 2.5 and for low currents we find that the vortex escapes, while for larger currents the vortex is reflected as an antivortex at one edge and the antivortex as a vortex at the other, leading to a stationary oscillatory state and to a non-zero time-averaged voltage. The escape and the reflection of a vortex at the array edges are qualitatively explained in terms of a coarse-grained model of a vortex interacting logarithmically with its image. We also discuss the case when the free boundaries are at 4545 degrees with respect to the direction of the vortex motion. Finally, we discuss the effect of self-induced magnetic fields by taking into account the full-range inductance matrix of the array, and find qualitatively equivalent results.Comment: 14 pages RevTex, 9 Postscript figure

    Macroscopic Quantum Tunneling of a Fluxon in a Long Josephson Junction

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    Macroscopic quantum tunneling (MQT) for a single fluxon moving along a long Josephson junction is studied theoretically. To introduce a fluxon-pinning force, we consider inhomogeneities made by modifying thickness of an insulating layer locally. Two different situations are studied: one is the quantum tunneling from a metastable state caused by a single inhomogeneity, and the other is the quantum tunneling in a two-state system made by two inhomogeneities. In the quantum tunneling from a metastable state, the decay rate is estimated within the WKB approximation. Dissipation effects on a fluxon dynamics are taken into account by the Caldeira-Leggett theory. We propose a device to observe quantum tunneling of a fluxon experimentally. Required experimental resolutions to observe MQT of a fluxon seem attainable within the presently available micro-fabrication technique. For the two-state system, we study quantum resonance between two stable states, i.e., macroscopic quantum coherence (MQC). From the estimate for dissipation coefficients due to quasiparticle tunneling, the observation of MQC appears to be possible within the Caldeira-Leggett theory.Comment: 30 pages LaTeX including 11 PS figures, using jpsj.sty. To be published on J. Phys. Soc. Jpn. Overestimates for damping amplitude is correcte

    Direct optical excitation of two and three magnons in α-Fe₂O₃

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    Direct excitation of two and three magnons is observed in midinfrared absorption and Raman scattering spectra of α-Fe₂O₃ crystals. These polarization characteristics and the spectra themselves are shown to be understood from group-theoretical point of view. The microscopic mechanism of three-magnon excitation is proposed in addition to that of well-known two-magnon excitation process
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