| 研究課題/領域番号 |
26390014
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| 研究機関 | 国立研究開発法人理化学研究所 |
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研究代表者 |
サーリコスキ ヘンリー 国立研究開発法人理化学研究所, 創発物性科学研究センター, 研究員 (50722245)
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| 研究分担者 |
多々良 源 国立研究開発法人理化学研究所, 創発物性科学研究センター, チームリーダー (10271529)
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| 研究期間 (年度) |
2014-04-01 – 2018-03-31
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| キーワード | spin / spintronics / topological / transport / mesoscopic / interference / spin-orbit / Berry |
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| 研究実績の概要 |
The project got outstanding results on mesoscopic semiconductor systems where a topological transition of the geometric phases was demonstrated and it was shown that the geometric phase involved in the process differed from that of the commonly used Berry and Aharonov-Anandan geometric phases. This novel emerging geometric phase was dubbed "the effective geometric phase" and a topological transition in spin interferometer devices was predicted. Intensive effort to show experimentally this transition is under way. This geometric phase was shown to have its classical counterpart that emerges e.g. in the precession of classical magnetic moments in an external magnetic field. The project members further showed that the topological transition can be observed in any two-level quantum system where the driving field changes topology from rotating to oscillating. Nuclear magnetic resonance (MRI) experiments were recently proposed as an alternative test-bed for such topological phenomena.
In the field of metallic spintronics in the project members studied current-driven dynamics of domain walls in synthetic ferrimagnetic nanowires. A very low threshold current density was predicted in systems anisotropically coupled domain-wall pairs are nonadiabatically driven. An effective theory was developed and shown to lead to huge reduction in threshold current densities in geometries where domain-walls are in-plane magnetized. In experiments almost an order of magnitude lower threshold current density was observed paving way for future low-power applications of domain-wall devices.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
Unexpected theoretical results were obtained in mesoscopic semiconductor systems that lead to theoretical predictions of related phenomena in other two-level quantum systems as well as in classical systems. Applications were predicted and a successful collaboration with experimentalist was completed.
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| 今後の研究の推進方策 |
The future work focuses on actual observation of the topological transition of the effective Berry phase in mesosopic devices. A collaboration with Nitta group at Tohoku university has been initiated on polygonal quantum ring devices. Initial results on this collaboration suggests that the observed features in experiments may be related to this topological transition. Effects of complex anisotropic spin-orbit fields on the electron spin dynamics are also under investigation.
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| 次年度使用額が生じた理由 |
It was decided to carry over a small amount of the grant to next fiscal year to present results in an international conference.
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| 次年度使用額の使用計画 |
The amount will be used to present results of the project at SPINTECH IX conference in June 4-8, 2017 in Fukuoka.
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