Faculty Profiles - SHIGETA Iduru

Iduru Shigeta, Osamu Murayama, Toru Hisamatsu, Masakazu Ito, Masahiko Hiroi . Measurements of spin polarization of Ru2-xFexCrSi Heusler alloys by Andreev reflection . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS470 S806 - S807 2010.12Reviewed International journal

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

We report spin polarization P of Ru2-xFexCrSi Heusler alloys by Andreev reflection technique. Ru2-xFexCrSi with the L2(1)-type structure is theoretically predicted to be half-metals in the wide range of the composition x. The experimental results of saturation moment in Fe-rich compounds measurements also support the theoretical prediction. We have measured the differential conductance of Ru2-xFexCrSi/Pb planar-type junctions. The P value of Ru2-xFexCrSi was determined by fitting the differential conductance with the modified Blonder-Tinkham-Klapwijk theory. The behavior of P was independent of the composition x in the Fe-rich region; P = 0.53 for x = 1.5 and P = 0.52 for x = 1.7, respectively. We have found that the spin polarization of Ru2-xFexCrSi in Fe-rich compounds was the similar values to Co-based Heusler alloys. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2010.01.044

Iduru Shigeta, Masakazu Ito . Advanced experiments of high-temperature superconductors for undergraduate students . Proceedings of the 4th International Symposium on Advances in Technology Education (ISATE2010) 1C6(1) - -7 2010.9Advanced experiments of high-temperature superconductors for undergraduate students

Masakazu Ito, Toru Hisamatsu, Tsugumi Rokkaku, Iduru Shigeta, Hirotaka Manaka, Norio Terada, Masahiko Hiroi . Low-temperature magnetic properties of Heusler compounds Ru_2-xFe_xCrSi (x = 0.1, 0.3, and 0.5) . Physical Review B82 024406(1) - -7 2010.7Low-temperature magnetic properties of Heusler compounds Ru_2-xFe_xCrSi (x = 0.1, 0.3, and 0.5)Reviewed

Masakazu Ito, Toru Hisamatsu, Tsugumi Rokkaku, Iduru Shigeta, Hirotaka Manaka, Norio Terada, Masahiko Hiroi . Low-temperature magnetic properties of Heusler compounds Ru2-xFexCrSi (x=0.1, 0.3, and 0.5) . PHYSICAL REVIEW B82 ( 2 ) 024406-1 - 024406-7 2010.7Reviewed International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We carried out magnetization M(T) and specific-heat C-P(T) measurements of the new Heusler compounds Ru2-xFexCrSi (x=0.1, 0.3, and 0.5), which exhibit spin-glass freezing. M(T) has peak- and irreversibility-type anomalies. The temperatures at which these anomalies appear have magnetic field dependence described by the Gabay-Toulouse and de Almeida-Thouless lines in the low-field range. For the magnetic specific heat C-m(T), we did not observe a discontinuity indicating long-range magnetic phase transition but a broad hump characteristic of spin-glass freezing. C-m(T) in the low-temperature range is described as a combination of linear- and quadratic-T terms. The quadratic-T dependence of C-m(T) is probably associated with excitation of the Ising component of the freezing spins.

DOI： 10.1103/PhysRevB.82.024406

Masahiko Hiroi, Tsugumi Rokkaku, Kazuhisa Matsuda, Toru Hisamatsu, Iduru Shigeta, Masakazu Ito, Takuo Sakon, Keiichi Koyama, Kazuo Watanabe, Shintaro Nakamura, Tsutomu Nojima, Tomohito Nakano, Lin Chen, Tetsuya Fujiwara, Yoshiya Uwatoko, Hirotaka Manaka, Norio Terada . Ferromagnetism and spin-glass transitions in the Heusler compounds Ru_2-xFe_xCrSi . Physical Review B79 224423(1) - -10 2009.6Ferromagnetism and spin-glass transitions in the Heusler compounds Ru_2-xFe_xCrSiReviewed

Hiroi Masahiko, Rokkaku Tsugumi, Matsuda Kazuhisa, Hisamatsu Toru, Shigeta Iduru, Ito Masakazu, Sakon Takuo, Koyama Keiichi, Watanabe Kazuo, Nakamura Shintaro, Nojima Tsutomu, Nakano Tomohito, Chen Lin, Fujiwara Tetsuya, Uwatoko Yoshiya, Manaka Hirotaka, Terada Norio . Ferromagnetism and spin-glass transitions in the Heusler compounds Ru2-xFexCrSi . PHYSICAL REVIEW B79 ( 22 ) 224423-1-10 2009.6Ferromagnetism and spin-glass transitions in the Heusler compounds Ru2-xFexCrSiReviewed International journal

Iduru Shigeta, Yasunari Tanuma, Yasuhiro Asano, Masahiko Hiroi, Yukio Tanaka . Midgap Andreev resonant state affected by superconducting proximity effect at junction interface of high-T_c cuprate attached to diffusive normal metal . Journal of Physics: Conference Series150 052235(1) - -4 2009.3Midgap Andreev resonant state affected by superconducting proximity effect at junction interface of high-T_c cuprate attached to diffusive normal metalReviewed

Yusuke Kondo, Iori Yano, Iduru Shigeta, Masakazu Ito, Masahiko Hiroi, Hirotaka Manaka, Norio Terada . Magnetic properties of the Heusler alloys Fe_2-xCo_xMnSi . Journal of Physics: Conference Series150 042099(1) - -4 2009.3Magnetic properties of the Heusler alloys Fe_2-xCo_xMnSiReviewed

Iduru Shigeta, Takehito Yokoyama, Yasuhiro Asano, Masahiko Hiroi, Yukio Tanaka . Effect of spin fluctuations on tunneling conductance in diffusive normal metal / conventional superconductor junctions . Journal of Physics: Conference Series150 052236(1) - -4 2009.3Effect of spin fluctuations on tunneling conductance in diffusive normal metal / conventional superconductor junctionsReviewed

Iduru Shigeta, Yasunari Tanuma, Yasuhiro Asano, Masahiko Hiroi, Yukio Tanaka . Tunneling study through analysis of spatial variations of the pair potential in diffusive normal metal/insulator/high-T-c superconductor junctions . JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS69 ( 12 ) 3042 - 3045 2008.12Reviewed International journal

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

We report how spatial variations of the pair potential with an anisotropic symmetry influence tunneling conductance spectra in diffusive normal metal/insulator/d(x2-y2)-wave superconductor (DN/I/DS) junctions. A zero-bias conductance peak (ZBCP) was observed for the (110)-oriented interface in Ag/SiO/Bi2Sr2CaCu2O8+delta (Bi-2212) planar junctions. The experimental ZBCP was analyzed by the circuit theory, which was improved by the introduction of spatial variations of the pair potential near the junction interface between a DN conductor and a DS electrode. Our experimental results are well explained by the extended circuit theory for DN/I/DS junctions. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2008.06.014

Iduru Shigeta, Takehito Yokoyama, Yasuhiro Asano, Fusao Ichikawa, Yukio Tanaka . Threshold temperatures of zero-bias conductance peak and zero-bias conductance dip in diffusive normal metal / superconductor junctions . Proceedings of the International Symposium on Mesoscopic Superconductivity and Spintronics 2006 (MS+S2006), World Scientific Publishers, Singapore 111 - 117 2008.6Threshold temperatures of zero-bias conductance peak and zero-bias conductance dip in diffusive normal metal / superconductor junctionsReviewed

Iduru Shigeta, Yasunari Tanuma, Yasuhiro Asano, Masahiko Hiroi, Yukio Tanaka . Tunneling study through analysis of spatial variations of the pair potential in diffusive normal metal / insulator / high-T_c superconductor junctions . Journal of Physics and Chemistry of Solids69 3042 - 3045 2008.1Tunneling study through analysis of spatial variations of the pair potential in diffusive normal metal / insulator / high-T_c superconductor junctionsReviewed

Iduru Shigeta, Takehito Yokoyama, Yasuhiro Asano, Fusao Ichikawa, Yukio Tanaka . Temperature dependence of tunneling conductance in diffusive normal metal / triplet superconductor junctions . Physica C: Superconductivity460-462 1319 - 1320 2007.9Temperature dependence of tunneling conductance in diffusive normal metal / triplet superconductor junctionsReviewed

Iduru Shigeta, Takehito Yokoyama, Yasuhiro Asano, Fusao Ichikawa, Yukio Tanaka . Temperature dependence of tunneling conductance in diffusive normal metal/triplet superconductor junctions . PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS460 1319 - 1320 2007.9Reviewed International journal

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

The thermal broadening effect on the tunneling conductance in diffusive normal metal/triplet superconductor (DN/TS) junctions is studied based on the Usadel equation under the generalized boundary condition. The zero-bias conductance peak (ZBCP) enhances in the antinodal direction, due to the coexistence of the proximity effect and the midgap Andreev resonant states at the DN/TS junction interface. It is found that the ZBCP is affected by the thermal broadening effect especially for tunnel junctions with the low transparency and the small Thouless energy. (c) 2007 Elsevier B.V. All tights reserved.

DOI： 10.1016/j.physc.2007.04.007

Iduru Shigeta, Yukio Tanaka, Fusao Ichikawa, Yasuhiro Asano . Smearing origin of zero-bias conductance peak in Ag-SiO-Bi₂Sr₂CaCu₂O_8+δ planar tunnel junctions: influence of diffusive normal metal verified with the circuit theory . The European Physical Journal B - Condensed Matter and Complex Systems54 ( 2 ) 141 - 149 2006.11Smearing origin of zero-bias conductance peak in Ag-SiO-Bi₂Sr₂CaCu₂O_8+δ planar tunnel junctions: influence of diffusive normal metal verified with the circuit theoryReviewed

I. Shigeta, Y. Tanaka, F. Ichikawa, Y. Asano . Smearing origin of zero-bias conductance peak in Ag-SiO-Bi2Sr2CaCu2O8+delta planar tunnel junctions: influence of diffusive normal metal verified with the circuit theory . EUROPEAN PHYSICAL JOURNAL B54 ( 2 ) 141 - 149 2006.11Reviewed International journal

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

We propose a new approach of smearing origins of a zero-bias conductance peak (ZBCP) in high-T-c superconductor tunnel junctions through the analysis based on the circuit theory for a d-wave pairing symmetry. The circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP frequently appears in line shapes for this theory, in which the total resistance was constructed by taking account of the effects between a d-wave superconductor and a diffusive normal metal (DN) at a junction interface, including the midgap Andreev resonant states (MARS), the coherent Andreev reflection (CAR) and the proximity effect. Therefore, we have analyzed experimental spectra with the ZBCP of Ag-SiO-Bi2Sr2CaCu2O8+delta (Bi-2212) planar tunnel junctions for the {110}-oriented direction by using a simplified formula of the circuit theory for d-wave superconductors. The fitting results reveal that the spectral features of the ZBCP are well explained by the circuit theory not only excluding the Dynes's broadening factor but also considering only the MARS and the DN resistance. Thus, the ZBCP behaviors are understood to be consistent with those of recent studies on the circuit theory extended to the systems containing d-wave superconductor tunnel junctions.

DOI： 10.1140/epjb/e2006-00440-2