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Author

Teruo Matsushita

Other affiliations: Kyushu University
Bio: Teruo Matsushita is an academic researcher from Kyushu Institute of Technology. The author has contributed to research in topics: Superconductivity & Flux pinning. The author has an hindex of 30, co-authored 384 publications receiving 3796 citations. Previous affiliations of Teruo Matsushita include Kyushu University.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a theoretical estimation of the contribution of 211 precipitates to flux pinning is also presented, and a value of pinning energy, U, comparable to that of conventional superconductors is obtained.

279 citations

Journal ArticleDOI
TL;DR: In this article, normal state conductivity in polycrystalline MgB2 bulk samples having a systematically varied packing factor was studied and the packing factor dependence of phonon term resistivity was found to be well explained by the three-dimensional site percolation model.
Abstract: Normal-state conductivity in polycrystalline MgB2 bulk samples having a systematically varied packing factor was studied The packing factor dependence of phonon term resistivity Δρ(T) = ρ(T)−ρ0 was found to be well explained by the three-dimensional site percolation model The low packing density of the samples and the wet impurity phases at grain boundaries are suggested to be the main causes of poor electrical connectivity in MgB2 Our model enables quantitative evaluations of the intrinsic resistivity inside the grains, the fraction of the active grains that can carry current and the anisotropy of the grains in polycrystalline samples The model predicts that the anomaly suppressed connectivity in rather weak-link-free MgB2 can be understood under a scenario of a percolation problem

139 citations

Journal ArticleDOI
Abstract: The irreversibility line in high‐temperature oxide superconductors is theoretically investigated from a viewpoint of dependence on the flux‐pinning strength and a general relation between the effective pinning potential and the critical current density is derived. It is shown that the irreversibility magnetic field at 77 K in strongly pinned oxide superconductors is sufficiently high for application.

106 citations

Journal ArticleDOI
TL;DR: In this article, the critical current density of superconducting polycrystalline MgB2 grains is determined by the electrical connectivity and flux pinning strength of grain boundaries.
Abstract: Electrical connectivity and flux pinning strength of grain boundaries are essential factors in determining the critical current density in superconducting polycrystalline MgB2. The effect of these factors is quantitatively investigated for a series of MgB2 bulk samples prepared by various methods. The electrical connectivity is evaluated using the percolation model and the obtained electrical connectivity is used for the estimation of the residual resistivity of superconducting MgB2 grains. The elementary pinning force of grain boundaries is evaluated using the theoretical result of Yetter et al based on the electron scattering mechanism with the residual resistivity. It is found that the critical current density is approximately proportional to the product of the electrical connectivity, the elementary pinning force of grain boundaries and the reciprocal grain size. This confirms that the critical current density is dominantly determined by the electrical connectivity and the flux pinning strength of grain boundaries. The flux pinning property in MgB2 under the condition of full electrical connectivity is compared with that in Nb3Sn. The obtained result shows that the flux pinning ability of pure MgB2 is comparable to or even higher than that of Nb3Sn, indicating a much higher potential in carbon-doped MgB2. This proves that the MgB2 is a promising superconductor for practical applications.

83 citations

Journal ArticleDOI
TL;DR: In this paper, small disk-shaped precipitates possibly regarded as strong flux pinning centers in the Y•Ba•Cu•O films were observed using transmission electron microscopy and the evaluation of Jc related to the concentration and configuration of the precipitates was in reasonable agreement with the measured Jc values.
Abstract: The Y‐Ba‐Cu‐O film prepared by chemical vapor deposition showed Tc=91.5 K and Bc2 (77.3 K)=60 T defined by zero resistance. The Jc values measured at 77.3 K were 7.8×105 A/cm2 at B=0 and 1.0×105 A/cm2 at 16 T, magnetic fields perpendicular to the c axis. Small disk‐shaped precipitates possibly regarded as strong flux pinning centers in the Y‐Ba‐Cu‐O films were observed using transmission electron microscopy. The evaluation of Jc related to the concentration and configuration of the precipitates was in reasonable agreement with the measured Jc values.

79 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors describe the properties of the triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and also by thermal fluctuations.
Abstract: Magnetic flux can penetrate a type-II superconductor in the form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons) each carrying a quantum of magnetic flux phi 0=h/2e. These tiny vortices of supercurrent tend to arrange themselves in a triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-Tc superconductors (HTSCs) also by thermal fluctuations. Many properties of the FLL are well described by the phenomenological Ginzburg-Landau theory or by the electromagnetic London theory, which treats the vortex core as a singularity. In Nb alloys and HTSCs the FLL is very soft mainly because of the large magnetic penetration depth lambda . The shear modulus of the FLL is c66~1/ lambda 2, and the tilt modulus c44(k)~(1+k2 lambda 2)-1 is dispersive and becomes very small for short distortion wavelengths 2 pi /k<< lambda . This softness is enhanced further by the pronounced anisotropy and layered structure of HTSCs, which strongly increases the penetration depth for currents along the c axis of these (nearly uniaxial) crystals and may even cause a decoupling of two-dimensional vortex lattices in the Cu-O layers. Thermal fluctuations and softening may `melt` the FLL and cause thermally activated depinning of the flux lines or ofthe two-dimensional `pancake vortices` in the layers. Various phase transitions are predicted for the FLL in layered HTSCs. Although large pinning forces and high critical currents have been achieved, the small depinning energy so far prevents the application of HTSCs as conductors at high temperatures except in cases when the applied current and the surrounding magnetic field are small.

866 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe the properties of the triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines and also by thermal fluctuations.
Abstract: Magnetic flux can penetrate a type-II superconductor in form of Abrikosov vortices. These tend to arrange in a triangular flux-line lattice (FLL) which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-$T_c$ supercon- ductors (HTSC's) also by thermal fluctuations. Many properties of the FLL are well described by the phenomenological Ginzburg-Landau theory or by the electromagnetic London theory, which treats the vortex core as a singularity. In Nb alloys and HTSC's the FLL is very soft mainly because of the large magnetic penetration depth: The shear modulus of the FLL is thus small and the tilt modulus is dispersive and becomes very small for short distortion wavelength. This softness of the FLL is enhanced further by the pronounced anisotropy and layered structure of HTSC's, which strongly increases the penetration depth for currents along the c-axis of these uniaxial crystals and may even cause a decoupling of two-dimensional vortex lattices in the Cu-O layers. Thermal fluctuations and softening may melt the FLL and cause thermally activated depinning of the flux lines or of the 2D pancake vortices in the layers. Various phase transitions are predicted for the FLL in layered HTSC's. The linear and nonlinear magnetic response of HTSC's gives rise to interesting effects which strongly depend on the geometry of the experiment.

812 citations

Journal ArticleDOI
01 Jul 1990-Nature
TL;DR: The anomalous magnetization characteristic, intra-grain granularity and the magnitude of the flux pinning in single crystals of YBa2Cu307-δ are intimately linked as mentioned in this paper.
Abstract: The anomalous magnetization characteristic, intra-grain granularity and the magnitude of the flux pinning in single crystals of YBa2Cu307–δ are shown to be intimately linked. As the nominal oxygen deficiency δ decreases towards zero, the flux pinning declines and the crystals lose their explicitly granular signature. As δ is seldom specifically controlled at levels below ˜0.05 in even the most carefully made materials, small oxygen deficiencies may contribute significantly to both the flux pinning and the weak-link properties.

620 citations

Journal ArticleDOI
TL;DR: In this article, experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation, are reviewed from a purely experimental perspective and discussed in the context of present phenomenological theories.
Abstract: We review experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation. This effect has its origin in motion of flux lines out of their pinning sites due to thermal activation or quantum tunneling. The combination of relatively weak flux pinning and high temperatures leads to rich properties that are unconventional in the context of low temperature superconductivity and that have been the subject to intense studies. The results are assessed from a purely experimental perspective and discussed in the context of present phenomenological theories. [S0034-6861(96)00403-5]

590 citations

Journal ArticleDOI
01 Feb 2000

393 citations