2005 Fiscal Year Final Research Report Summary
Physics of Spin-Triplet Superconductivity
| Project/Area Number |
13852004
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| Research Category |
Grant-in-Aid for Scientific Research (S)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Kyoto University |
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Principal Investigator |
MAENO Yoshiteru Kyoto University, International Innovation Center, Professor, 国際融合創造センター, 教授 (80181600)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIDA Kenji Kyoto University, Department of Physics, Graduate of Science, Associate Professor, 大学院・理学研究科, 助教授 (90243196)
YAGUCHI Hiroshi Kyoto University, Department of Physics, Graduate School of Science, Associate Professor Professor, 大学院・理学研究科, 助手 (30314173)
NAKATSUJI Satoru Kyoto University, Department of Physics, Graduate School of Science, Lecture, 大学院・理学研究科, 講師 (70362431)
YAMADA Kosaku Kyoto University, Department of Physics, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (90013515)
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| Project Period (FY) |
2001 – 2005
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| Keywords | spin-triplet superconductivity / ruthenate / Sr_2RuO_4 / odd parity / NMR / time-reversal symmetry / strongly correlated system / superconducting gap |
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| Research Abstract |
We firmly established for the first time that a superconductor with its electrons paired in a spin-triplet state actually exists. Through extensive investigations focusing on the ruthenate superconductor Sr_2RuO_4,we obtained a number of new key concepts in the study of superconductivity :
(1) Determination of the superconducting multi-gaps : We devised a method of determining the superconducting gap on each of the Fermi surface. For Sr_2RuO_4,we understand the physical origin of its multi-gap structure based on the spin-triplet symmetry and the spin fluctuations.
(2) Determination of the Cooper-pair spin state : By nuclear magnetic resonance (NMR), we determined that the triplet spins lie in the RuO_2 plane, but that they can be rotated by weak magnetic fields.
(3) Confirmation of odd parity : We fabricated a pi-junction SQUID (Superconducting QUantum Interference Device) consisting of Sr_2RuO_4 and an s-wave superconductor AuIn, and demonstrated that the parity of the superconducting wave function of Sr_2RuO_4 is odd, a requirement for the spin-triplet superconductivity.
(4) Construction of the theoretical framework of superconducting mechanisms : We have succeeded in constructing a general theoretical framework of superconducting mechanism based on Coulomb repulsion among the strongly correlated electrons. By applying it to a detailed realistic model of Sr_2RuO_4,we are able to derive that the spin-triplet pairing is more stable than other states.
We also discovered superconductivity in silver-lead oxide, Ag_5Pb_2O_6,clarified the mechanism of the Mott transition and orbital ordering in (Ca,Sr)_2RuO_4,and revealed the metamagnetic quantum critical phenomenon in Sr_3Ru_2O_7. We sponsored the international symposium on "Spin-Triplet Superconductivity and Ruthenate Physics", attended by most of the active researchers in this field, including over 20 researches from 8 abroad.
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