| Project/Area Number |
15K05210
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Mathematical physics/Fundamental condensed matter physics
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| Research Institution | Kyoto University |
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Principal Investigator |
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| Project Period (FY) |
2015-04-01 – 2019-03-31
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| Project Status |
Completed (Fiscal Year 2018)
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| Budget Amount *help |
¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000)
Fiscal Year 2017: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2016: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2015: ¥2,600,000 (Direct Cost: ¥2,000,000、Indirect Cost: ¥600,000)
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| Keywords | スピングラス / レプリカ対称性の破れ / 臨界現象 / 非平衡緩和 / エイジング現象 / 記憶効果 / 若返り効果 / 動的臨界現象 / Griffiths相 / 長距離相互作用 / 磁場中相転移 / 磁場中転移 / 温度カオス |
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| Outline of Final Research Achievements |
We have experimentally investigated on a nature of the spin glass state in long-range RKKY Ising spin glasses (SG). According to the mean-field theory of SG, the SG state is a ordered state where the replica-symmetry is broken. However, it is an open question whether the replica-symmetry is broken in "real spin glass materials". To answer this question, we have examined the replica-symmetry-breaking (RSB) in model magnets of the long-range RKKY Ising spin glass, (R,Y)Ru2Si2 (R = Dy, Tb, Gd) and Dy(Co,Ru)2Si2. In these compounds, the spin glass state survives even in the presence of magnetic field, which have been verified by our careful dynamic scaling analysis of the ac susceptibility in field. Furthermore, nonequilibrium magnetization response with various zero-field-cooling protocols exhibits characteristics which can be well understood by assuming hierarchical development of energy-barriers. These findings are good evidences of the RSB in the long-range RKKY Ising spin glasses.
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| Academic Significance and Societal Importance of the Research Achievements |
レプリカ対称性の破れ(RSB)は、正負ランダムに分布した相互作用をもつスピン系の基底状態であるスピングラスを記述する重要な概念であり、スピングラス状態の複雑性の基礎となる。スピングラスの平均場理論ではRSBが起こっていることは厳密に分かっているが、現実のスピングラス物質(やそれと等価な統計力学モデル)でのRSBについては結論は出ておらず、むしろRSBを否定する結果の方が有力視されている。本課題の実験結果は、ある種の長距離相互作用が働く系では3次元系でもRSBが起こることを強く示す結果であり、現実のスピングラス状態の本質を明らかにする重要な結果であると言える。
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