| Project/Area Number |
17540318
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Niigata University |
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Principal Investigator |
NEMOTO Yuichi Niigata University, Institute of Science and Technology, Associate Professor, 自然科学系, 助教授 (10303174)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEDA Naoya Niigata University, Institute of Science and Technology, Professor, 自然科学系, 教授 (80242171)
GOTO Terutaka Niigata University, Institute of Science and Technology, Professor, 自然科学系, 教授 (60134053)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 2005: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Keywords | Strongly Correlated Electron Systems / Ultrasound / Rattling / Quadrupole / Clathrate Compounds / Superconductivity / Low-Temperature Experiment / Solid State Physics / 磁性 / 低温 / スクッテルダイト / 低温物性 |
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| Research Abstract |
1)We previously observed ultrasonic disperSi_6n due to rattling in heavy-fermion superconductor PrOs_4Sb_<12>. Furthermore, elastic softening proportional to the 1/T was found below 4 K down to T_c=1.85 K, which is attributed to off-center tunneling of Pr ion in a cage. These results support that the strong correlation between rattling/tunneling and heavy-fermion and it's superconductivity in PrOs_4Sb_<12>.
2)We have made ultrasonic experiments of the Ru substitutional Pr(Os_<1-x>RuX)_4Sb_<12>. As a result, ultrasonic disperSi_6n becomes weak with more substitution of Ru concentration and completely disappears in BCS superconductor PrRu_4Sb_<12>. We proposed that the coupling between the off-center tunneling and conduction electrons will cause the heavy-fermion state and superconductivity in PrOs_4Sb_<12>.
3)We have examined LaOs_4Sb_<12> without 4f-electron in order to investigate the correlation between rattling and 4f electrons. Ultrasonic disperSi_6n in C_<11> was clearly observed, t
… More
hat means rattling appears without 4f-electron. We conclude that the coupling between off-center mode and surrounding conduction electrons is crucial for the rattling and tunneling.
4)We have measured elastic constants of NdOs_4Sb_<12> with three 4f electrons. Two distinct ultrasonic disperSi_6ns around 40 K and 15 K were observed in C_<11>. This result indicates that multiple structure of anharmonic potential is formed in a cage as it were, illustrated by two deferent activation energy E and characteristic time τ_0 of the rattling in NdOs_4Sb_<12>.
5)We have observed elastic softening of C_<11> and C_<44> proportional to the 1/T at low temperatures in NdOs_4Sb_<12>. According to the analysis using quadrupolar susceptibility, we confirmed that the ground state of the crystal field levels of 4f^3 electronic state is Γ_<67> quartet in NdOs_4Sb_<12>.
6)We have performed ultrasonic measurements of isomorphic compound La_3Pd_<20>Si_6 and Ce_3Pd_<20>Si_6 to study rattling and tunneling. As a result, no ultrasonic dispersions were found in La_3Pd_<20>Si_6 and Ce_3Pd_<20>Si_6 contrary to our previous results of R_3Pd_<20>_Ge6. Here we report that the importance of the conduction bands as well as clathrate structure for the occurrence of rattling and tunneling.
7)We have observed elastic softening of (C_<11>-C_<12>)/2 and C_<44> proportional to the 1/T at low temperatures in Ce_3Pd_<20>Si_6. We obtained crystal field levels by use of quadrupolar susceptibility to be a Γ_8 quarter ground at 8c site and a Γ_7 doublet ground at 4a site, respectively. Furthermore, we revealed that the presence of antiferro-quadrupolar ordering phase in magnetic fields. Less
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