Valence-skip mechanism of superconductivity in doped Dirac electron system

• Project/Area Number: 18K03540
• 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: Okayama University
• Principal Investigator: Kobayashi Kaya 岡山大学, 異分野基礎科学研究所, 准教授 (60424090)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Project Status: Completed (Fiscal Year 2020)
• Budget Amount: ¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000); Fiscal Year 2020: ¥390,000 (Direct Cost: ¥300,000、Indirect Cost: ¥90,000); Fiscal Year 2019: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000); Fiscal Year 2018: ¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000)
• Keywords: バレンススキップ超伝導 / 超伝導 / ディラック物質 / ディラック電子系

Outline of Final Research Achievements

We study cubic superconductor Ag1-xSn1+xSe2 for its possible Dirac electrons in superconductivity and for its uniqueness being a valence skipping superconductor candidate. The synthesis of single crystals and polycrystalline crystals of wide variety are performed and confirmed that superconducting transition temperatures, Tcs, vary depending on the ratio between Ag and Sn. Due to the discontinuous valence state changes of Sn, 2+ and 4+, charge dispropornation in spatial forms is expected. It is also expected to have two distinct Sn-Se distances, however, the observed electronic states in nuclear magnetic resonance (NMR) show only one state, while distinct two states observed in X-ray photoemission spectroscopy (XPS). The contradicting results suggests the valence skipping behavior in the superconductivity depend on the timescale and the two valence states overlap and distributed uniformly.

Academic Significance and Societal Importance of the Research Achievements

今回得られた結果は強相関系で実現するバレンススキップ超伝導に関して初めて実験的にバレンススキップを確認することが出来たなど、バレンススキップ超伝導に関して得られた重要な結果である。また、これまで考えられてきたような、空間的に局在した電子が動き出す描像ではなく、電子は一見金属的に見えるもののスナップショット的な測定を行うことによって分裂した状態の重ね合わせとみることもできるなど、超伝導発現に関して新しい局面をもたらすものであると考えられる。

Research Products

• [Int'l Joint Research] Sapienza University of Rome(イタリア)
• [Int'l Joint Research] Navel Research Lab./Argonne Natl. Lab./Hofsta University(米国)
• [Int'l Joint Research] サピエンツァ大学(イタリア)
• [Journal Article] Optical signatures of phase transitions and structural modulation in elemental tellurium under pressure (2020)
  • Author(s): Rodriguez Diego、Tsirlin Alexander A.、Biesner Tobias、Ueno Teppei、Takahashi Takeshi、Kobayashi Kaya、Dressel Martin、Uykur Ece
  • Journal Title: Physical Review B Volume: 101 Issue: 17 Pages: 174101-174101
  • DOI: 10.1103/physrevb.101.174104
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Superconductivity in Bi2-xSbxTe3-ySey (x = 1.0 and y = 2.0) under pressure (2020)
  • Author(s): He Tong、Yang Xiaofan、Taguchi Tomoya、Zhi Lei、Miyazaki Takafumi、Kobayashi Kaya、Akimitsu Jun、Ishii Hirofumi、Liao Yen-Fa、Goto Hidenori、Eguchi Ritsuko、Kubozono Yoshihiro
  • Journal Title: Journal of Physics: Condensed Matter Volume: 32 Issue: 46 Pages: 465702-465702
  • DOI: 10.1088/1361-648x/abaad2
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Time-reversal invariant and fully gapped unconventional superconducting state in the bulk of the topological compound Nb0.25Bi2Se3 (2020)
  • Author(s): Das Debarchan、Kobayashi K.、Smylie M. P.、Mielke C.、Takahashi T.、Willa K.、Yin J.-X.、Welp U.、Hasan M. Z.、Amato A.、Luetkens H.、Guguchia Z.
  • Journal Title: Physical Review B Volume: 102 Issue: 13 Pages: 134514-134514
  • DOI: 10.1103/physrevb.102.134514
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Two Linear Regimes in Optical Conductivity of a Type-I Weyl Semimetal: The Case of Elemental Tellurium (2020)
  • Author(s): Rodriguez Diego、Tsirlin Alexander A.、Biesner Tobias、Ueno Teppei、Takahashi Takeshi、Kobayashi Kaya、Dressel Martin、Uykur Ece
  • Journal Title: Physical Review Letters Volume: 124 Issue: 13 Pages: 136402-136402
  • DOI: 10.1103/physrevlett.124.136402
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Superconductivity in 5d transition metal Laves phase SrIr2 (2020)
  • Author(s): R. Horie, K. Horigane, S. Nishiyama, M. Akimitsu, K. Kobayashi, S. Onari, T. Kambe, Y. Kubozono, J. Akimitsu
  • Journal Title: Journal of Physics: Condensed Matter Volume: 32 Issue: 17 Pages: 175703-175703
  • DOI: 10.1088/1361-648x/ab6a2e
  • Peer Reviewed
• [Journal Article] Unusual electronic state of Sn in AgSnSe2 (2020)
  • Author(s): Naijo Y.、Hada K.、Furukawa T.、Itou T.、Ueno T.、Kobayashi K.、Mazin I. I.、Jeschke H. O.、Akimitsu J.
  • Journal Title: Physical Review B Volume: 101 Issue: 7 Pages: 075134-075134
  • DOI: 10.1103/physrevb.101.075134
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Superconducting Properties of AgSnSe2 Studied by 77Se-NMR and 119Sn-NMR (2020)
  • Author(s): Watanabe K.、Naijo Y.、Hada K.、Furukawa T.、Itou T.、Ueno T.、Kobayashi K.、Akimitsu J.
  • Journal Title: JPS Conf. Proc. Volume: 30 Pages: 11057-11057
  • DOI: 10.7566/jpscp.30.011057
  • Peer Reviewed
• [Journal Article] Nodeless superconducting gap in the candidate topological superconductor Sn1?xInxTe for x=0.7 (2020)
  • Author(s): Smylie M. P.、Kobayashi Kaya、Takahashi T.、Chaparro C.、Snezhko A.、Kwok W.-K.、Welp U.
  • Journal Title: Physical Review B Volume: 101 Issue: 9 Pages: 94513-94513
  • DOI: 10.1103/physrevb.101.094513
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Fermi level tuning of Ag-doped Bi2Se3 topological insulator (2019)
  • Author(s): Uesugi Eri、Uchiyama Takaki、Goto Hidenori、Ota Hiromi、Ueno Teppei、Fujiwara Hirokazu、Terashima Kensei、Yokoya Takayoshi、Matsui Fumihiko、Akimitsu Jun、Kobayashi Kaya、Kubozono Yoshihiro
  • Journal Title: Scientific Reports Volume: 9 Issue: 1 Pages: 5376-5376
  • DOI: 10.1038/s41598-019-41906-7
  • NAID: 120006777514
  • Peer Reviewed / Open Access
• [Journal Article] Determination of the local structure of Sr2-xMxIrO4 (M = K, La) as a function of doping and temperature (2018)
  • Author(s): Kensei Terashima, Eugenio Paris, Eduardo Salas-Colera, Laura Simonelli, Boby Joseph, Takanori Wakita, Kazumasa Horigane, Masanori Fujii, Kaya Kobayashi, Rie Horie, Jun Akimitsu, Yuji Muraoka, Takayoshi Yokoya and Naurang Lal Saini
  • Journal Title: Phys.Chem.Chem.Phys. Volume: 20 Issue: 36 Pages: 23783-23788
  • DOI: 10.1039/c8cp03756f
  • Peer Reviewed / Int'l Joint Research
• [Presentation] Ag0.8Sn1.2Se2 単結晶の顕微光電子分光 (2021)
  • Author(s): 脇田高徳, 片岡範行, Li Ya Jun, 室隆桂之, 小林夏野, 上野哲平, 秋光純, 村岡祐治, Naurang L. Saini, 横谷尚睦
  • Organizer: 日本物理学会
• [Presentation] (Pb1-xTlx)Te超伝導体における不純物サイトのNMR緩和率とナイトシフト測定から見た電荷近藤効果 (2020)
  • Author(s): 堀川瑠星, 八島光晴, 椋田秀和, 三宅和正A, 村上博成B, P. WalmsleyC, P. Giraldo-GalloC, T. Geballe, I. Fisher, 高橋武士, 小林夏野
  • Organizer: 日本物理学会
• [Presentation] Possible valence skipping superconductivity in doped Dirac metal (2019)
  • Author(s): Teppei Ueno, Takanori Wakita, Tetsuya Furukawa, Tetsuaki Itou, Takayoshi Yokoya, Jun Akimitsu, Kaya Kobayashi
  • Organizer: APS March Meeting 2019
  • Int'l Joint Research
• [Presentation] Ag1-xSn1+xSe2（x = 0.0, 0.1, 0.2, 0.25 及び1.0）のEXAFS解析 (2019)
  • Author(s): 脇田高徳, Eugenio Paris, 小林夏野, 寺嶋健成, Muammer Yasin Hacisalioglu, 上野哲平, Federica Bondino, Elena Magnano, Igor Pis, Luca Olivi, 秋光純, 村岡祐治, 横谷尚睦, Naurang L. Saini
  • Organizer: 日本物理学会第74回年次大会(2019年)
• [Presentation] 119Sn-NMR測定によるValence Skipping候補物質AgSnSe2の超伝導相電子状態の検証 (2019)
  • Author(s): 内條雄介, 羽田健吾, 古川哲也, 伊藤哲明, 上野哲平, 小林夏野, 秋光純
  • Organizer: 日本物理学会第74回年次大会(2019年)
• [Presentation] AgSnSe2のNMRから見た超伝導相電子状態の解明 (2018)
  • Author(s): 内條雄介, 羽田健吾, 古川哲也, 伊藤哲明, 上野哲平, 小林夏野, 秋光純
  • Organizer: 日本物理学会2018年秋季大会
• [Presentation] NMRから見たValence Skipping候補物質AgSnSe2の金属相電子状態 (2018)
  • Author(s): 羽田健吾, 内條雄介, 古川哲也, 伊藤哲明, 上野哲平, 小林夏野, 秋光純
  • Organizer: 日本物理学会2018年秋季大会