Faculty Profiles - SHIGETA Iduru

Iduru Shigeta, Yukio Tanaka, Fusao Ichikawa, Yasuhiro Asano, Satoshi Kashiwaya . Zero-bias conductance peak reduction by diffusive normal metal in high-T_c superconductor tunnel junctions . Journal of Physics and Chemistry of Solids66 1401 - 1404 2005.8Zero-bias conductance peak reduction by diffusive normal metal in high-T_c superconductor tunnel junctionsReviewed

Shigeta, I, Y Tanaka, F Ichikawa, Y Asano, S Kashiwaya . Zero-bias conductance peak reduction by diffusive normal metal in high-T-c superconductor tunnel junctions . JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS66 ( 8-9 ) 1401 - 1404 2005.8Reviewed International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We report investigations of the smearing origin about a zero-bias conductance peak (ZBCP) observed in high-T-c superconductor (HTSC) tunnel junctions from the point of view of the circuit theory analysis for d-wave superconductors. The ZBCP enhancement was measured in Bi2Sr2CaCU2O8+delta-SiO-Ag planar tunnel junctions only for ab-plane directions. On the other hand, the circuit theory has been recently generalized from conventional superconductors to unconventional superconductors. The analysis in terms of the circuit theory reveals that the tunneling spectral behaviors of the ZBCP were well explained even when the Dynes's broadening factor was excluded from a tunneling spectral formula. Thus, the smearing effect in the ZBCP is understood by the influence of a diffusive normal metal resistance in the systems of HTSC tunnel junctions. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.05.019

Iduru Shigeta, Yukio Tanaka, Fusao Ichikawa, Yasuhiro Asano, Satoshi Kashiwaya . Circuit theory analysis of ab-plane tunnel junctions of unconventional superconductor Bi₂Sr₂CaCu₂O_8+δ . Proceedings of the International Symposium on Mesoscopic Superconductivity and Spintronics 2004 (MS+S2004), World Scientific Publishers, Singapore 161 - 166 2005.7Circuit theory analysis of ab-plane tunnel junctions of unconventional superconductor Bi₂Sr₂CaCu₂O_8+δReviewed

Shigeta, I, T Abiru, K Abe, A Nishida, Y Matsumoto . Temperature and field dependence of magnetization of MgB2 polycrystals . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS392 359 - 363 2003.10Reviewed International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We present magnetization properties of magnesium diboride (MgB2). MgB2 polycrystals were fabricated by using the vapor transport method inside a sealed stainless tube. The critical current density J(c) was estimated from the magnetization hysteresis DeltaM by using the Bean model. The temperature dependence of J(c) (T) showed a linear behavior below 15 K and deviated from such behavior in the higher temperature region. This behavior indicates that a flux creep effect influences the wide temperature range for the MgB2 polycrystals. Furthermore, small values of DeltaM show that the pinning force density F-p is very weak. The temperature dependence of the upper critical field H-c2 (T) was also obtained and revealed a linear behavior far from T-c. From our experimental results, we conclude that the MgB2 polycrystals are of good quality with less pinning centers, compared to the commercially available MgB2 powder. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0921-4534(03)01049-9

A Nishida, C Taka, Shigeta, I . Effects of Y substitution on the temperature and field dependence of magnetic hystereses in YxGd1-xBa2Cu3O7-delta . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS392 349 - 352 2003.10Reviewed International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Effects of Y substitution on the magnetic hystereses are investigated in Y-substituted YxGd1-xBa2Cu3O7-delta ceramics. Magnetizations are first measured at respective constant temperatures, where the hysteresis DeltaM is estimated by the magnetization difference between field increase and decrease. When the variations of DeltaM for the identical field against temperatures are examined, DeltaM is found to obey DeltaM = A exp[-T/T-0] with the single To for a given field. The characteristic temperature T-0 is in the range of 10-30 K, and the field dependence is compared with the function: H-1/n. The field dependence of T-0 for the x = 0.2 (nominal) sample is larger than that for the pure Gd123 ceramics of x = 0, reflecting larger T-0 at lower magnetic fields. This is owing to larger DeltaM at higher temperatures and lower fields in the Y-substituted system. Improvement of the intergrain coupling by the Y substitution is discussed in comparison with magnetic behaviors in the pure sample. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0921-4534(03)00848-7

Y Matsumoto, Shigeta, I, T Abiru, Y Terasaki, T Akune, N Sakamoto . Critical current density and flux pinning characteristics of powdered MgB2 specimens . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS388 163 - 164 2003.5Reviewed International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Field and temperature dependence of magnetization and also time dependent magnetization (flux creep) of powdered MgB2 specimens have been measured by using a SQUID magnetometer in the temperature range of 4.5 less than or equal to T less than or equal to 37 K and under the field up to 1 T. Scaling plots of normalized pinning force density F-p/F-p max as a function of normalized flux density B/B-max in the temperature range of 25 less than or equal to T less than or equal to 37 K showed that a two dimensional pinning is dominant for the flux pinning of the specimens. Another distinct feature is that a linear reduction of J(c) with increasing temperature at temperatures lower than 30 K and a quadratic decrease at higher temperatures than 35 K have been observed. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02707-7

Shigeta, I, F Ichikawa, T Fukami, T Aomine . Observation of a large superconducting gap in Bi-based cuprates by tunneling spectroscopy . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS388 291 - 292 2003.5Reviewed International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We report that a large superconducting gap has been observed in some tunneling spectra of Bi2Sr2CaCu2O8+delta (Bi2212). The observed gap magnitude is roughly twice as large as those of the recent studies of Bi2212. Magnetic susceptibility measurements reveal that the single crystals retain a single phase of Bi2212. Therefore, the experimental results suggest that the large gap arises by way of the superconductor-insulator-superconductor (SIS) tunnel junction, due to the junction interface of the crystal boundary. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(03)00627-0

A Nishida, S Teshima, C Taka, Shigeta, I . Field- and temperature-dependent magnetic hysteresis in GdBa2Cu3O7-delta ceramics . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS388 419 - 420 2003.5Reviewed International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Magnetic hysteresis measurements are performed in GdBa2Cu3O7-delta ceramics, and effects of magnetic field, temperature and substitution are studied. The hysteresis DeltaM is found to decay exponentially with temperature: DeltaM proportional to exp[-T/T-0]. The activation temperature T-0 varies mildly around 20 K, which seems to depend on the magnetic field as H-1/n. Substitution tends to increase DeltaM at lower fields. The results are examined in relation to ceramic nature of the sample. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02549-2

Shigeta, I, F Ichikawa, T Aomine . Temperature dependence of zero-bias conductance peak in Bi2Sr2CaCu2O8+delta-SiO-Ag planar tunnel junctions . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS378 316 - 319 2002.10Reviewed International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We present the temperature dependence of tunneling spectra of as-grown Bi2Sr2CaCu2O8+delta single crystals. An enhancement of the zero-bias conductance peak (ZBCP) was observed for the ab-plane tunnel junctions. The ZBCP has appeared below the bulk superconducting critical temperature T-c. This experimental result suggests that the ZBCP obviously arises by way of the superconducting gap and not the pseudogap. This result is consistent with recent studies of the Andreev bound states model for d-wave superconductors. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)01434-X

I. Shigeta, T. Uchida, Y. Tominari, T. Arai, F. Ichikawa, T. Fukami, T. Aomine, V. M. Svistunov . In-plane tunneling spectroscopy in Bi2Sr2CaCu2O8+δ-SiO-Ag planar junctions . Physica C: Superconductivity and its Applications357-360 205 - 207 2001Reviewed International coauthorship International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We report the experimental results of quasiparticle tunneling using Bi2Sr2CaCu2O8+δ-SiO-Ag planar junctions. We have measured the (0 0 1)-, (1 0 0)- and (1 1 0)-oriented junctions. For the in-plane ab oriented junctions, a reproducible zero bias conductance peak has been observed. We have analyzed the data by using the extended Andreev bound states model for d-wave superconductors and have considered the roughness effect by averaging over in-plane directions. The experimental results are consistent with the theoretical calculations. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00207-6

Shigeta, I, T Uchida, Y Tominari, T Arai, F Ichikawa, T Fukami, T Aomine, VM Svistunov . Zero bias conductance peak enhancement in Bi2Sr2CaCu2O8+delta-SiO-Ag planar tunnel junctions . JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN69 ( 9 ) 2743 - 2746 2000.9Reviewed International coauthorship International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

We report the experimental results of quasiparticle tunneling using Bi2Sr2CaCu2O8+delta (BSCCO)-SiO-Ag planar junctions. For the {001}-oriented junctions, we have measured a well-known V-shaped gap structure expected for d-wave superconductors. For the {100}- and {110}-oriented junctions, a reproducible zero bias conductance peak (ZBCP) enhancement has been observed. The temperature dependence of the ZBCP is also presented. The ZBCP was observed below T-c. Our results are consistent with those of recent studies on the Andreev reflection between a d-wave superconductor and a normal metal.

DOI： 10.1143/JPSJ.69.2743