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Search Results: 1 - 10 of 362783 matches for " J. -i. Shimoyama "
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Possible interaction between thermal electrons and vibrationally excited N2 in the lower E-region
K.-I. Oyama, M. Shimoyama, J. Y. Liu,C. Z. Cheng
Annales Geophysicae (ANGEO) , 2011,
Abstract: As one of the tasks to find the energy source(s) of thermal electrons, which elevate(s) electron temperature higher than neutral temperature in the lower ionosphere E-region, energy distribution function of thermal electron was measured with a sounding rocket at the heights of 93–131 km by the applying second harmonic method. The energy distribution function showed a clear hump at the energy of ~0.4 eV. In order to find the reason of the hump, we conducted laboratory experiment. We studied difference of the energy distribution functions of electrons in thermal energy range, which were measured with and without EUV radiation to plasma of N2/Ar and N2/O2 gas mixture respectively. For N2/Ar gas mixture plasma, the hump is not clearly identified in the energy distribution of thermal electrons. On the other hand for N2/O2 gas mixture, which contains vibrationally excited N2, a clear hump is found when irradiated by EUV. The laboratory experiment seems to suggest that the hump is produced as a result of interaction between vibrationally excited N2 and thermal electrons, and this interaction is the most probable heating source for the electrons of thermal energy range in the lower E-region. It is also suggested that energy distribution of the electrons in high energy part may not be Maxwellian, and DC probe measures the electrons which are non Maxwellian, and therefore "electron temperature" is calculated higher.
Universal relationship between crystallinity and irreversibility field of MgB2
A. Yamamoto,J. Shimoyama,S. Ueda,Y. Katsura,I. Iwayama,S. Horii,K. Kishio
Physics , 2005, DOI: 10.1063/1.1937991
Abstract: The relationship between irreversibility field, Hirr, and crystallinity of MgB2 bulks including carbon substituted samples was studied. The Hirr was found to increase with an increase of FWHM of MgB2 (110) peak, which corresponds to distortion of honeycomb boron sheet, and their universal correlation was discovered even including carbon substituted samples. Excellent Jc characteristics under high magnetic fields were observed in samples with large FWHM of (110) due to the enhanced intraband scattering and strengthened grain boundary flux pinning. The relationship between crystallinity and Hirr can explain the large variation of Hirr for MgB2 bulks, tapes, single crystals and thin films.
Superconducting order parameter in heavily overdoped $Bi_2 Sr_2 Ca Cu_2 O_{8+δ}$: a global quantitative analysis
R. H. He,D. L. Feng,H. Eisaki,J. -i. Shimoyama,K. Kishio,G. D. Gu
Physics , 2004, DOI: 10.1103/PhysRevB.69.220502
Abstract: A systematic analysis of the complex lineshape at $(\pi,0)$ of heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is presented. We show that a coherent component in the quasi-particle excitation is correlated with the superfluid density throughout the entire doping range and suggest it is a direct measure of the order parameter of high temperature superconductors.
Disorder and thermally driven vortex-lattice melting in La{2-x}Sr{x}CuO{4} crystals
Y. Radzyner,A. Shaulov,Y. Yeshurun,I. Felner,K. Kishio,J. Shimoyama
Physics , 2001, DOI: 10.1103/PhysRevB.65.100503
Abstract: Magnetization measurements in La{2-x}Sr{x}CuO{4} crystals indicate vortex order-disorder transition manifested by a sharp kink in the second magnetization peak. The transition field exhibits unique temperature dependence, namely a strong decrease with temperature in the entire measured range. This behavior rules out the conventional interpretation of a disorder-driven transition into an entangled vortex solid phase. It is shown that the transition in La{2-x}Sr{x}CuO{4} is driven by both thermally- and disorder-induced fluctuations, resulting in a pinned liquid state. We conclude that vortex solid-liquid, solid-solid and solid to pinned-liquid transitions are different manifestations of the same thermodynamic order-disorder transition, distinguished by the relative contributions of thermal and disorder-induced fluctuations.
Evidence for Nodal superconductivity in Sr$_{2}$ScFePO$_{3}$
K. A. Yates,I. T. M. Usman,K. Morrison,J. D. Moore,A. M. Gilbertson,A. D. Caplin,L. F. Cohen,H. Ogino,J. Shimoyama
Physics , 2009, DOI: 10.1088/0953-2048/23/2/022001
Abstract: Point contact Andreev reflection spectra have been taken as a function of temperature and magnetic field on the polycrystalline form of the newly discovered iron-based superconductor Sr2ScFePO3. A zero bias conductance peak which disappears at the superconducting transition temperature, dominates all of the spectra. Data taken in high magnetic fields show that this feature survives until 7T at 2K and a flattening of the feature is observed in some contacts. Here we inspect whether these observations can be interpreted within a d-wave, or nodal order parameter framework which would be consistent with the recent theoretical model where the height of the P in the Fe-P-Fe plane is key to the symmetry of the superconductivity. However, in polycrystalline samples care must be taken when examining Andreev spectra to eliminate or take into account artefacts associated with the possible effects of Josephson junctions and random alignment of grains.
Evidence for an energy scale for quasiparticle dispersion in Bi_2Sr_2CaCu_2O_8
P. V. Bogdanov,A. Lanzara,S. A. Kellar,X. J. Zhou,E. D. Lu,W. Zheng,G. Gu,K. Kishio,J. -I. Shimoyama,Z. Hussain,Z. X. Shen
Physics , 2000, DOI: 10.1103/PhysRevLett.85.2581
Abstract: Quasiparticle dispersion in $Bi_{2}Sr_{2}CaCu_{2}O_{8}$ is investigated with improved angular resolution as a function of temperature and doping. Unlike the linear dispersion predicted by the band calculation, the data show a sharp break in dispersion at $50\pm10$ $meV$ binding energy where the velocity changes by a factor of two or more. This change provides an energy scale in the quasiparticle self-energy. This break in dispersion is evident at and away from the d-wave node line, but the magnitude of the dispersion change decreases with temperature and with increasing doping.
ARPES study of Pb doped Bi_2Sr_2CaCu_2O_8 - a new Fermi surface picture
P. V. Bogdanov,A. Lanzara,X. J. Zhou,S. A. Kellar,D. L. Feng,E. D. Lu,J. -I. Shimoyama,K. Kishio,Z. Hussain,Z. X. Shen
Physics , 2000, DOI: 10.1103/PhysRevB.64.180505
Abstract: High resolution angle resolved photoemission data from Pb doped Bi_2Sr_2CaCu_2O_8 (Bi2212) with suppressed superstructure is presented. Improved resolution and very high momentum space sampling at various photon energies reveal the presence of two Fermi surface pieces. One has the hole-like topology, while the other one has its van Hove singularity very close to (pi,0), its topology at some photon energies resembles the electron-like piece. This result provides a unifying picture of the Fermi surface in the Bi2212 compound and reconciles the conflicting reports.
Fermi Surface of Bi2212: a Systematic Revisit and Identification of Almost Perfectly Nested Fermi Surface Segments
D. L. Feng,W. J. Zheng,K. M. Shen,D. H. Lu,F. Ronning,J. -i. Shimoyama,K. Kishio,G. Gu,D. Van der Marel,Z. -X. Shen
Physics , 1999,
Abstract: The Fermi surface of the Bi2212 system is systematically studied using a variety of photon energies. In addition to reconciling the conflicting reports on the Fermi surface of this important material, we identify almost perfectly nested Fermi surface segments parallel to the $(1,0)$ or $(0,1)$ direction. This general yet long overlooked feature of the Fermi surface is intriguingly similar to the Fermi surface of the $La_{1.48}Nd_{0.4}Sr_{0.12}CuO_4$ system.
Signature of Superfluid Density in the Single-Particle Excitation Spectrum of Bi2Sr2CaCu2O8+delta
D. L. Feng,D. H. Lu,K. M. Shen,C. Kim,H. Eisaki,A. Damascelli,R. Yoshizaki,J. -i. Shimoyama,K. Kishio,G. D. Gu,S. Oh,A. Andrus,J. O'Donnell,J. N. Eckstein,Z. -X. Shen
Physics , 2000, DOI: 10.1126/science.289.5477.277
Abstract: We report that the doping and temperature dependence of photoemission spectra near the Brillouin zone boundary of Bi2Sr2CaCu2O8+delta exhibit unexpected sensitivity to the superfluid density. In the superconducting state, the photoemission peak intensity as a function of doping scales with the superfluid density and the condensation energy. As a function of temperature, the peak intensity shows an abrupt behavior near the superconducting phase transition temperature where phase coherence sets in, rather than near the temperature where the gap opens. This anomalous manifestation of collective effects in single-particle spectroscopy raises important questions concerning the mechanism of high-temperature superconductivity.
Bilayer Splitting in the Electronic Structure of Heavily Overdoped Bi2Sr2CaCu2O8+d
D. L. Feng,N. P. Armitage,D. H. Lu,A. Damascelli,J. P. Hu,P. Bogdanov,A. Lanzara,F. Ronning,K. M. Shen,H. Eisaki,C. Kim,Z. -X. Shen,J. -i. Shimoyama,K. Kishio
Physics , 2001, DOI: 10.1103/PhysRevLett.86.5550
Abstract: The electronic structure of heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is investigated by angle-resolved photoemission spectroscopy. The long-sought bilayer band splitting in this two-plane system is observed in both normal and superconducting states, which qualitatively agrees with the bilayer Hubbard model calculations. The maximum bilayer energy splitting is about 88 meV for the normal state feature, while it is only about 20 meV for the superconducting peak. This anomalous behavior cannot be reconciled with the quasiparticle picture.
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