Study on odd frequency Cooper pairs at junction interfaces in tunneling phenomena

2011 Fiscal Year Final Research Report

• Project/Area Number: 21740259
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Single-year Grants
• Research Field: Condensed matter physics II
• Research Institution: Kagoshima University
• Principal Investigator: SHIGETA Iduru 鹿児島大学, 大学院・理工学研究科, 助教 (30370050)
• Project Period (FY): 2009 – 2011
• Keywords: ハーフメタル / 超伝導体 / アンドレーエフ反射 / スピン分極率 / 奇周波数クーパー対

Research Abstract

In this work, I have studied on odd frequency Cooper pairs at junction interfaces between a ferromagnet and a superconductor. I have clarified several topics as follows:
1. I synthesized Heusler alloys Co_<2-x> Fe_xMnSi and Ru_<2-x> Fe_xCrSi, which are expected as half-metal by the first-principles band calculations. Those materials are candidates of half-metal.
2. The spin polarization of Co_<2-x> Fe_xMnSi is independent of composition x and is equal to approximately 50%.
3. The spin polarization of Ru_<2-x> Fe_xCrSi is maximum value of 63% in the case of x=1. 8.
4. I succeed in fabricating fully-epitaxial NbN/Co_2MnSi and NbN/Co_2FeSi bilayers and those nano-junctions in order to trap the odd frequency Cooper pairs.
5. I observed a large zero-bias peak in differential conductance of NbN/Co_2MnSi nano-junctions. The phenomenon are not explained by the modified Blonder-Tinkham-Klapwijk(BTK) model and indicates generations of odd frequency pairs at the junction interface.

Research Products

• [Journal Article] Magnetization and spin polarization of Co_<2-x> Fe_x MnSi Heusler alloys (2012)
  • Author(s): I. Shigeta, S. Urakawa, M. Ito, M. Hiroi
  • Journal Title: Journal of Physics : Conference Series(accepted)
  • Peer Reviewed
• [Journal Article] Spin polarized conductance in ferromagnet/insulator/conventional superconductor junctions (2012)
  • Author(s): I. Shigeta, Y. Tanaka, Alexander A. Golubov, Masahiko Hiroi
  • Journal Title: Journal of Physics : Conference Series(accepted)
  • Peer Reviewed
• [Journal Article] Spin polarization of Fe-rich ferromagnetic compounds in Ru_<2-x> Fe_xCrSi Heusler alloys (2011)
  • Author(s): I. Shigeta, O. Murayama, T. Hisamatsu, A. Brinkman, A. A. Golubov, Y. Tanaka, M. Ito, H. Hilgenkamp, M. Hiroi
  • Journal Title: Journal of Physics and Chemistry of Solids Volume: 72 Pages: 604-607
  • DOI: DOI:10.1016/j.jpcs.2010.10.062
  • Peer Reviewed
• [Journal Article] Magnetic properties of Ru-rich Ru_<2-x> Fe_xCrZ (2011)
  • Author(s): M. Hiroi, S. Nakashima, K. Nakao, T. Rokkaku, M. Ito, I. Shigeta, H. Manaka, N. Terada
  • Journal Title: Journal of Superconductivity and Novel Magnetism Volume: 24 Pages: 753-756
  • DOI: DOI:10.1007/s10948-010-0967-6
  • Peer Reviewed
• [Journal Article] Measurements of spin polarization of Ru_<2-x> Fe_xCrSi Heusler alloys by Andreev reflection (2010)
  • Author(s): I. Shigeta, O. Murayama, T. Hisamatsu, M. Ito, M. Hiroi
  • Journal Title: Physica C Volume: 470 Pages: S806-S807
  • DOI: DOI:10.1016/j.physc.2010.01.044
  • Peer Reviewed
• [Journal Article] Effect of spin fluctuations on charge transport in diffusive normal metal/d-wave superconductor junctions (2010)
  • Author(s): I. Shigeta, T. Yokoyama, Y. Asano, M. Hiroi, Y. Tanaka
  • Journal Title: Physica C Volume: 470 Pages: S854-S856
  • DOI: DOI:10.1016/j.physc.2009.12.015
  • Peer Reviewed
• [Journal Article] Low-temperature magnetic properties of Heusler compounds Ru_<2-x> Fe_xCrSi (2010)
  • Author(s): M. Ito, T. Hisamatsu, T. Rokkaku, I. Shigeta, H. Manaka, N. Terada, M. Hiroi
  • Journal Title: Physical Review Volume: B82 Pages: 024406(1)-(7)
  • DOI: DOI:10.1103/PhysRevB.82.024406
  • Peer Reviewed
• [Journal Article] Ferromagnetism and spin-glass transitions in the Heusler compounds Ru_<2-x> Fe_xCrSi (2009)
  • Author(s): M. Hiroi, T. Rokkaku, K. Matsuda, T. Hisamatsu, I. Shigeta, M. Ito, T. Sakon, K. Koyama, K. Watanabe, S. Nakamura, T. Nojima, T. Nakano, L. Chen, T. Fujiwara, Y. Uwatoko, H. Manaka, N. Terada
  • Journal Title: Physical Review Volume: B79 Pages: 224423(1)-(10)
  • DOI: DOI:10.1103/PhysRevB.79.224423
  • Peer Reviewed
• [Journal Article] Midgap Andreev resonant state affected by superconducting proximity effect at junction interface of high-T_c cuprate attached to diffusive normal metal (2009)
  • Author(s): I. Shigeta, Y. Tanuma, Y. Asano, M. Hiroi, Y. Tanaka
  • Journal Title: Journal of Physics Volume: 150 Pages: 052235(1)-(4)
  • DOI: DOI:10.1088/1742-6596/150/5/052236
  • Peer Reviewed
• [Journal Article] Effect of spin fluctuations on tunneling conductance in diffusive normal metal/conventional superconductor junctions (2009)
  • Author(s): I. Shigeta, T. Yokoyama, Y. Asano, M. Hiroi, Y. Tanaka
  • Journal Title: Journal of Physics : Conference Series Volume: 150 Pages: 052236(1)-(4)
  • DOI: DOI:10.1088/1742-6596/150/5/052235
  • Peer Reviewed
• [Presentation] Magnetization and spin polarization of Co_<2-x> Fe_xMnSi Heusler alloys (2011)
  • Author(s): I. Shigeta, S. Urakawa, M. Ito, M. Hiroi
  • Organizer: The 26th International Conference on Low Temperature Physics(LT26)
  • Place of Presentation: the Beijing International Convention Center(BICC), Beijing, China
  • Year and Date: 20110810-17
• [Presentation] Spin polarized conductance in ferromagnet/insulator/conventional superconductor junctions (2011)
  • Author(s): I. Shigeta, Y. Tanaka, A. A. Golubov, M. Hiroi
  • Organizer: The 26th International Conference on Low Temperature Physics(LT26)
  • Place of Presentation: the Beijing International Convention Center(BICC), Beijing, China
  • Year and Date: 20110810-17
• [Presentation] Spin polarization of Fe-rich ferromagnetic compounds in Ru_<2-x> Fe_xCrSi Heusler alloys (2010)
  • Author(s): I. Shigeta, O. Murayama, T. Hisamatsu, A. Brinkman, A. A. Golubov, Y. Tanaka, M. Ito, H. Hilgenkamp, M. Hiroi
  • Organizer: The 9th International Conference on Spectroscopies in Novel Superconductors(SNS2010)
  • Place of Presentation: Fudan University, Shanghai, China
  • Year and Date: 20100523-28
• [Presentation] Measurements of spin polarization of Ru_<2-x> Fe_xCrSi Heusler alloys by Andreev reflection (2009)
  • Author(s): I. Shigeta, O. Murayama, T. Hisamatsu, M. Ito, M. Hiroi
  • Organizer: The 9th International Conference on Materials and Mechanisms of Superconductivity(M^2S-IX)
  • Place of Presentation: Keio Plaza Hotel, Tokyo, Japan
  • Year and Date: 20090907-12
• [Presentation] Effect of spin fluctuations on charge transport in diffusive normal metal/d-wave superconductor junctions (2009)
  • Author(s): I. Shigeta, T. Yokoyama, Y. Asano, M. Hiroi, Y. Tanaka
  • Organizer: The 9th International Conference on Materials and Mechanisms of Superconductivity(M^2S-IX)
  • Place of Presentation: Keio Plaza Hotel, Tokyo, Japan
  • Year and Date: 20090907-12
• [Presentation] Spin polarization measurements of Ru_<2-x> Fe_xCrSi Heusler alloys in Fe-rich ferromagnetic region by Andreev reflection (2009)
  • Author(s): I. Shigeta, O. Murayama, T. Hisamatsu, M. Ito, M. Hiroi
  • Organizer: New Directions of Superconducting Nanostructures 2009(NDSN2009)
  • Place of Presentation: Environmental Studies Hall, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, Japan
  • Year and Date: 20090904-05
• [Remarks]
  • URL: http://www.sci.kagoshima-u.ac.jp/～shigeta/