Superconductivity in new type of noncentrosymmetric crystal structure compounds

• Project/Area Number: 19K03755
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: National Institute for Materials Science
• Principal Investigator: ISOBE Masaaki 国立研究開発法人物質・材料研究機構, 機能性材料研究拠点, 上席研究員 (10354309)
• Co-Investigator(Kenkyū-buntansha): 新井 正男 国立研究開発法人物質・材料研究機構, 技術開発・共用部門, ステーション長 (40222723)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Project Status: Completed (Fiscal Year 2021)
• Budget Amount: ¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000); Fiscal Year 2021: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2020: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2019: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
• Keywords: 超伝導 / 強相関電子系 / 空間反転対称性 / 電子構造 / 強相関 / 磁性

Outline of Research at the Start

空間反転対称性が破れた結晶系では、超伝導クーパー対の対称性がパリティ混合状態になると考えられている。
最近、本課題の申請者は、対称中心の無い新型の結晶構造を有する新しい超伝導体BaIrSi2（Tc ~ 6 K）を合成発見した。本研究では、新物質BaIrSi2の詳細な物性解析を行い、その電子構造と超伝導状態を明らかにする。
高圧合成による良質試料を用いて、結晶構造と超伝導特性を詳細に決定する。また、第一原理計算により、電子構造を明らかにする。さらに、NMR、mSR測定などを行い、超伝導ギャップ構造を明らかにする。

Outline of Final Research Achievements

Noncentrosymmetric superconductivity refers to the superconductivity that occurs in spatially asymmetric systems which have no inversion center in the crystal structure. It has been theoretically predicted that in such a superconducting system, odd parity component is mixed in the Cooper pair wavefunction and that the upper critical magnetic field may become huge. In order to clarify the mechanism of noncentrosymmetric superconductivity, we studied the superconducting state in the new compound BaIrSi2.
As a result, it was found that BaIrSi2 is a BCS-type intermediate coupling superconductor. Furthermore, we conducted new material search based on knowledge obtained from the physical properties and electronic structure in BaIrSi2. We succeeded in discovering new type of superconductors BaRhSi2 and Li2IrSi2.

Academic Significance and Societal Importance of the Research Achievements

超伝導の社会利用をより広く実現するには、転移温度（Tc）・上部臨界磁場（Hc2）・臨界電流（Jc）のブレークスルー的な改善が欠かせない。それには、既存物質の材料化の工夫だけでは限界があるため、物質固有の特性（物性）が極めて優れた物質を新たに見いだす必要がある。即ち、固体の電子論に立ち返った超伝導発現メカニズムの解明に関する研究が必要である。
本研究課題では、“空間反転対称性の破れた超伝導”に着目し、その物性解明と新物質開発に取り組んだ。このような基礎研究を多く積み上げることで、将来的に、既存物質の性能を大幅に凌駕する新しい超伝導物質の発見に繋がると考える。

Research Products

• [Journal Article] BaIrSi2: A 5d Electron System Superconductor with a New Type of Noncentrosymmetric Crystal Structure (2020)
  • Author(s): Isobe Masaaki、Kimoto Koji、Arai Masao、Kolodiazhnyi Taras、Kanke Yasushi、Takayama-Muromachi Eiji
  • Journal Title: JPS Conf. Proc. Volume: 30
  • DOI: 10.7566/jpscp.30.011179
  • Peer Reviewed / Open Access
• [Journal Article] Substitution Effect of the Electronic Structure of Layered Iridium Oxides from Hard X-ray Photoemission Spectroscopy (2020)
  • Author(s): Tsuda Shunsuke、Sugiura Shiori、Hirose Hishiro T.、Kikugawa Naoki、Ueda Shigenori、Isobe Masaaki、Uji Shinya
  • Journal Title: JPS Conf. Proc. Volume: 30
  • DOI: 10.7566/jpscp.30.011144
  • Peer Reviewed / Open Access
• [Journal Article] Static and dynamic spin properties in the quantum triangular lattice antiferromagnet Ag2CoO2 (2020)
  • Author(s): Yoshida H. K.、Dissanayake S. E.、Christianson A. D.、dela Cruz C. R.、Cheng Y.-Q.、Okamoto S.、Yamaura K.、Isobe M.、Matsuda M.
  • Journal Title: Physical Review B Volume: 102 Issue: 2 Pages: 024445-024445
  • DOI: 10.1103/physrevb.102.024445
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Magnetic excitations affected by spin-lattice coupling in the S=32 triangular lattice antiferromagnet Ag2CrO2 (2020)
  • Author(s): Matsuda Masaaki、Dissanayake Sachith E.、Yoshida Hiroyuki K.、Isobe Masaaki、Stone Matthew B.
  • Journal Title: Physical Review B Volume: 102 Issue: 21
  • DOI: 10.1103/physrevb.102.214411
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Partially disordered state with short-range spin correlation in S=5/2 classical triangular antiferromagnet Ag2FeO2 (2020)
  • Author(s): Yoshida H. K.、Matsuda M.、Stone M. B.、dela Cruz C. R.、Furubayashi T.、Onoda M.、Takayama-Muromachi E.、Isobe M.
  • Journal Title: Physical Review Research Volume: 2 Issue: 4
  • DOI: 10.1103/physrevresearch.2.043211
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Responsive Four‐Coordinate Iron(II) Nodes in FePd(CN) 4 (2020)
  • Author(s): Ohtani Ryo、Matsunari Hiromu、Yamamoto Takafumi、Kimoto Koji、Isobe Masaaki、Fujii Kotaro、Yashima Masatomo、Fujii Susumu、Kuwabara Akihide、Hijikata Yuh、Noro Shin‐ichiro、Ohba Masaaki、Kageyama Hiroshi、Hayami Shinya
  • Journal Title: Angewandte Chemie International Edition Volume: 59 Issue: 43 Pages: 19254-19259
  • DOI: 10.1002/anie.202008187
  • Peer Reviewed / Open Access
• [Journal Article] Enhanced visible-light photocatalytic activity of anatase-rutile mixed-phase nano-size powder given by high-temperature heat treatment (2020)
  • Author(s): Ishigaki Takamasa、Nakada Yusuke、Tarutani Naoki、Uchikoshi Tetsuo、Tsujimoto Yoshihiro、Isobe Masaaki、Ogata Hironori、Zhang Chenning、Hao Dong
  • Journal Title: Royal Society Open Science Volume: 7 Issue: 1 Pages: 191539-191539
  • DOI: 10.1098/rsos.191539
  • Peer Reviewed / Open Access
• [Journal Article] Superconductivity in a new layered triangular-lattice system Li2IrSi2 (2019)
  • Author(s): K. Horigane, K. Takeuchi, D. Hyakumura, R. Horie, T. Sato, T. Muranaka, K. Kawashima, H. Ishii H, Y. Kubozono, S. Orimo, M. Isobe, J. Akimitsu
  • Journal Title: New Journal of Physics Volume: 21 Issue: 9 Pages: 093056-093056
  • DOI: 10.1088/1367-2630/ab4159
  • Peer Reviewed / Open Access
• [Presentation] 空間反転対称性の破れた新型結晶構造を有する5d電子系新超伝導体BaIrSi2 (2019)
  • Author(s): 磯部雅朗、木本浩司、新井正男、室町英治
  • Organizer: 日本物理学会2019年秋季大会
• [Presentation] μSR法で見た反転対称性を持たない結晶構造を持つBaIrSi2の超伝導状態 (2019)
  • Author(s): 宮崎一輝、髭本亘、網田裕斗、伊藤孝、磯部雅朗
  • Organizer: 日本物理学会2019年秋季大会
• [Presentation] BaIrSi2: A 5d Electron System Superconductor with a New Type of Noncentrosymmetric Crystal Structure (2019)
  • Author(s): Masaaki ISOBE, Koji KIMOTO, Masao ARAI, and Eiji TAKAYAMA-MUROMACHI
  • Organizer: International Conference on Strongly Correlated Electron Systems 2019 (SCES 2019)（国際学会）
  • Int'l Joint Research
• [Remarks] 物質・材料研究機構 機能性材料研究拠点 上席研究員
  • URL: https://www.nims.go.jp/research/researcher/masaaki-isobe.html
• [Remarks] 物質・材料研究機構・機能性材料研究拠点・強相関物質グループ
  • URL: http://www.nims.go.jp/research/group/strong-correlated-materials/