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Journal Articles

A Trial usage of microprobes for improvement of a scanning SQUID microscope

Okayasu, Satoru; Kokubo, Nobuhito*; Kakeya, Itsuhiro*

Physica C, 463-465, p.294 - 296, 2007/10

 Times Cited Count:0 Percentile:0(Physics, Applied)

A scanning SQUID microsope is a powerful tool for direct observations of vortices. Magnetic sensitivity is high enough, but spacial resolution is limited by the size of pickup coils. To improve the spacial resolution, a trial usage of microprobe on the pickupcoil was achieved. Preliminary results show the improvement of sensitivity, not spacial resolution.

Journal Articles

Strong pairing and microscopic inhomogeneity of lattice fermion systems

Yamada, Susumu; Machida, Masahiko; Ohashi, Yoji*; Matsumoto, Hideki*

Physica C, 463-465, p.103 - 106, 2007/10

 Times Cited Count:0 Percentile:0(Physics, Applied)

In order to study an interplay between electronic inhomogeneity and superconductivity as seen in High-Tc cuprates as well as to predict effects of optical lattice in atomic Fermi gases, we numerically examine attractive Hubbard model in the absence of the translation symmetry. For the purpose, we systematically calculate the particle density profile for both 1-D and 2-D attractive Hubbard models with harmonic potential wells using the exact diagonalization and the density-matrix renormalization group methods. The numerical results reveal that fine inhomogeneous zigzag patterns universally emerge in the 1-D model case and the zig-zag structure becomes checkerboard type in the 2-D one. Moreover, it is numerically and theoretically found that such inhomogeneities are caused by double occupation component, i.e., pairs tightly bound on a site. These calculation results are universal for many-body Fermi-particle systems on lattice. We predict that the behavior described above is widely observable from atomic Fermi gas to strong coupled superconductors including High-Tc superconductors.

Journal Articles

Development of large current superconductors using high performance Nb$$_{3}$$Sn strand for ITER

Koizumi, Norikiyo; Isono, Takaaki; Hamada, Kazuya; Nunoya, Yoshihiko; Matsui, Kunihiro; Nabara, Yoshihiro; Okuno, Kiyoshi

Physica C, 463-465, p.1319 - 1326, 2007/10

 Times Cited Count:10 Percentile:46.38(Physics, Applied)

Both mass production technique of strand having high critical current enough to recover the degradation observed in the model coil conductor and also trial fabrication of the ITER-TF cable and conduit section were successfully performed. Critical current degradation by spatially periodic transverse load was both experimentally and numerically studied. The simulation results show that the transverse resistance among the filaments significantly affect on degree of the degradation. The test results also showed that the developed strand has almost the same resistance against the transverse load as the TFMC strand. Therefore, the small degradation of the TF conductor, i.e., stable operation of the TF conductor is preliminarily anticipated.

Journal Articles

Theory for collective macroscopic tunneling in high-$$T$$$$_{rm c}$$ intrinsic Josephson junctions

Machida, Masahiko; Koyama, Tomio*

Physica C, 463-465, p.84 - 88, 2007/10

 Times Cited Count:2 Percentile:13.24(Physics, Applied)

On the basis of the theory for the capacitive coupling in intrinsic Josephson junctions (IJJ's), we theoretically study the macroscopic quantum tunneling in the switching dynamics into the voltage states in IJJ. The effective action obtained by using the path integral formalism reveals that the capacitive coupling splits each of the lowest and higher quantum levels, which are given inside Josephson potential barrier of the single junction derived by dropping off the coupling, into quantum levels composed of the number of junction ($$N$$). This level splitting can cause multiple low-frequency Rabi-oscillations and enhance the switching probability compared to the conventional Caldeira-Leggett theory. Furthermore, a possibility as a naturally built-in multi-qubit is discussed.

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