2002 Fiscal Year Final Research Report Summary
Study on magnetic excitons in uranium-based heavy fermion superconductors
| Project/Area Number |
12440091
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Nagoya University |
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Principal Investigator |
SATO Noriaki Nagoya University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (30170773)
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| Co-Investigator(Kenkyū-buntansha) |
ASO Naofumi University of Tokyo, Institute for Solid State Physics, Assistant Professor, 物性研究所, 助手 (40313118)
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| Project Period (FY) |
2000 – 2002
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| Keywords | uranium compounds / heavy fermions / superconductivity / magnetic exciton / UPd_2Al_3 / UNi_2Al_3 / UGe_2 / URu_2Si_2 |
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| Research Abstract |
(1) Magnetic exciton mediated superconductivity in UPd_2Al_3
We succeeded in preparing single crystals of high quality, and measured physical properties of those crystals to obtain information of the magnetism and superconductivity. We discovered the existence of two components in inelastic neutron scattering spectra, and we safely ascribed the lower energy component to quasiparticle excitations and the higher energy one to magnetic excitons. We proposed a new model, that is called "dual nature of 5f electrons", to analyze the data. We finally found the strong coupling between the two components. We also found that the spectra are consistent with spectra obtained from tunneling experiments within the Eliashberg equation framework. From these results, we pointed out that the superconducting attractive interaction is mediated by exchange of bosonic magnetic excitons. This result was reported in Nature, 410(2001)340-343.
(2) Magnetism and superconductivity in UNi_2Al_3
In UNi_2Al_3 that has
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the same crystal structure as UPd_2Al_3, the antiferromagnetic ordered state also coexists with superconductivity. We carried out NMR experiments, and found that the Knight shift shows no reduction below the superconducting transition temperature, in remarkably contrast with the isotropic reduction in UPd_2Al_3. From this result together with the absence of the Pauli limiting effect in the temperature dependence of the superconducting upper critical field, we concluded that the spin-triplet (odd parity) paring is formed.
(3) Magnetism and superconductivity in UGe_2 and URu_2Si_2
We prepared single crystals to investigate the correlation of ferromagnetism and superconductivity in UGe_2. We measured the dc magnetization and ac magnetic susceptibility under high pressures, and we found that the superconducting volume fraction grows with increasing pressure. From this, we suggested that the superconductivity coexists in a competitive way with the ferromagnetism.
We also carried out the dilatation measurements under high pressure for single crystals of URu_2Si_2. We found an anomaly in the thermal expansion coefficient that corresponds to the phase transition between hidden and antiferromagnetic order. Less
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