2022 Fiscal Year Final Research Report
Observation of nonreciprocal charge transport phenomena caused by current-induced breaking of the time-reversal and space-inversion symmetries
| Project/Area Number |
20K14408
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| Research Category |
Grant-in-Aid for Early-Career Scientists
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| Allocation Type | Multi-year Fund |
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| Review Section |
Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
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| Research Institution | Kyushu University (2022)
The University of Tokyo (2020-2021) |
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Principal Investigator |
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | 超伝導電流 / テラヘルツ / 非相反応答 / 反転対称性の破れ / 磁束量子 |
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| Outline of Final Research Achievements |
Supercurrents are dissipationless flows of superconducting electrons that break both time-reversal and space-inversion symmetries. Therefore, superconductors under supercurrent injection exhibit specific electromagnetic responses known as nonreciprocal transport phenomena, resulting from the symmetry breaking.
In this project, we investigated nonlinear optical responses of superconductors by observing the transmitted terahertz (THz) pulses for high-intensity and narrowband THz irradiations under three methods of supercurrent injection: (1) direct injection of a DC supercurrent, (2) dynamical induction of a transient current using THz pulses, and (3) static induction of a shielding current using weak magnetic fields.
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| Free Research Field |
物性実験
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| Academic Significance and Societal Importance of the Research Achievements |
電流は一般に時間反転対称性を破る。通常の散逸的な電流においては、不可逆性（irreversibility）という意味で対称性が破れるが、超伝導電流の場合は、磁場と同様な平衡場の１種として、文字どおりの時間反転対称性（time-reversal symmetry）を破ると期待される。
本研究では、空間反転対称性が破れた物質が磁場下で発生する第２高調波発生が、超伝導電流存在下の超伝導体によっても発生することを実験的に示し、上記の解釈を提案した。加えて、光学測定時に超伝導電流を注入する手法を複数実証し、現在理論研究が進められている超伝導電流が誘起する相転移や特異な光学応答の測定に向けて道を拓いた。
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