2023 Fiscal Year Final Research Report
Investigation of quantum critical phenomena in two-dimensional superconductors by thermoelectric response
| Project/Area Number |
20K14413
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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 | Tokyo Institute of Technology |
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Principal Investigator |
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| Project Period (FY) |
2020-04-01 – 2024-03-31
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| Keywords | ２次元超伝導体 / 熱電効果 / 超伝導-絶縁体転移 / 量子渦(渦糸) / 超伝導ゆらぎ / 異常金属状態 / 量子臨界 |
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| Outline of Final Research Achievements |
In two-dimensional superconductors, quantum liquid and condensation of magnetic flux lines, which are caused by strong quantum fluctuations in the very low-temperature and high-field region, have been suggested by electrical resistance. However, conclusive evidence has not yet been obtained. To verify these phenomena, in addition to the electrical resistance measurements, in this study we conducted the thermoelectric effect measurements down to 0.1 K, which can clearly detect the motion of the magnetic flux lines. In a 12 nm-thick amorphous MoxGe1-x thin film, we revealed that the anomalous residual resistance observed in the high-field region is caused by the quantum liquid of flux lines. Furthermore, by measuring a 10 nm-thick sample over a wide temperature-field range, we revealed the boundary line between the thermal and quantum fluctuation regions, demonstrating that the origin of the quantum liquid of flux lines is due to the existence of a quantum critical point.
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| Free Research Field |
超伝導，低温物理，ナノ物理
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| Academic Significance and Societal Importance of the Research Achievements |
磁束線の量子液体は，2次元超伝導体で普遍的に生じる超伝導-絶縁体転移に付随する現象である．通常，2次元超伝導体や層状超伝導体では物質固有の現象と2次元効果が混ざって観測されるため，アモルファス超伝導薄膜という単純な系で得られた知見は，これらを分離するために重要である．
現在研究されている超伝導量子ビットでは磁束線一本の量子性を利用しているのに対し，本研究では超伝導体を貫く磁束線が集団的に示す量子性を明らかにした．このことは，量子計算機としての機能が期待される冷却原子気体のような量子多体系が，固体中にも形成される可能性を示唆しており，新たな量子デバイス開発の指針となると期待される.
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