2016 Fiscal Year Research-status Report
Topological Transitions in Spin Transport in Nanostructures
| Project/Area Number |
26390014
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
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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| Co-Investigator(Kenkyū-buntansha) |
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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| Project Period (FY) |
2014-04-01 – 2018-03-31
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| Keywords | spin / spintronics / topological / transport / mesoscopic / interference / spin-orbit / Berry |
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| Outline of Annual Research Achievements |
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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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
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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| Strategy for Future Research Activity |
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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| Causes of Carryover |
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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| Expenditure Plan for Carryover Budget |
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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[Journal Article] Synthetic ferrimagnet nanowires with very low critical current density for coupled domain wall motion2017
Author(s)
Serban Lepadatu, Henri Saarikoski, Robert Beacham, Maria Jose Benitez, Thomas A. Moore, Gavin Burnell, Satoshi Sugimoto, Daniel Yesudas, May C. Wheeler, Jorge Miguel, Sarnjeet S. Dhesi, Damien McGrouther, Stephen McVitie, Gen Tatara & Christopher H. Marrows
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Journal Title
Scientific Reports
Volume: 7
Pages: 1640
DOI
Peer Reviewed / Open Access / Int'l Joint Research
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[Journal Article] Spin resonance under topological driving fields2017
Author(s)
Andres Reynoso, Jose Pablo Baltanas, H. Saarikoski, J. Enrique Vazquez Lozano, Junsaku Nitta, Diego Frustaglia
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Journal Title
New Journal of Physics
Volume: to appear (accepted)
Pages: 106477
DOI
Peer Reviewed / Open Access / Int'l Joint Research / Acknowledgement Compliant
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