| Project/Area Number |
17K14337
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Multi-year Fund |
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| Research Field |
Condensed matter physics II
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
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| Project Period (FY) |
2017-04-01 – 2019-03-31
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| Project Status |
Completed (Fiscal Year 2018)
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| Budget Amount *help |
¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000)
Fiscal Year 2018: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2017: ¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000)
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| Keywords | ネルンスト効果 / 渦糸 / 磁束量子 / 超伝導薄膜 / 超伝導-絶縁体転移 / 量子相転移 / ボースグラス / 量子凝縮 / ボーズグラス / 第二種超伝導体 / 量子渦 / 熱電効果 / 超伝導絶縁体転移 |
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| Outline of Final Research Achievements |
Using thermoelectric measurements, we study the Bose condensation of vortices, which is predicted at very low temperature and high field in an insulating phase of disordered two-dimensional (2D) superconductors. In the preliminary experiment above 5 K using a three-dimensional superconducting amorphous MoxGe1-x film, clear thermoelectric signals were observed in a thermal vortex-liquid (VL) phase. In the experiment down to 100 mK for a 2D film, clear signals from vortices were observed in the low-temperature and low-field regime, corresponding to a metallic quantum VL phase. With increasing the field, however, these signals decrease and vanish toward a critical field of the metal-insulator transition. This is consistent with the observation that a negative magnetoresistance just above the transition, indicative of the vortex condensation, is very small. This probably results from weak disorder in the sample. We will continue our study using samples with stronger disorder.
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| Academic Significance and Societal Importance of the Research Achievements |
原子層近くまで薄くした超伝導体に極低温で磁場を加えていくと、超伝導が完全に壊れて絶縁体となる前に、超伝導体内を貫く磁束（渦糸）が量子効果によって凍らず液体状態になった金属や絶縁体状態が現れることが予想されている。特に絶縁体相では多数の磁束が１つの波に凝縮した特異な現象が予想され、それが検証できれば大きな学術的意義をもつ。本研究ではこの現象を最も明確に検出できる、熱流に対する磁束の応答を測定する実験手法を確立させた。その結果、磁束が量子液体状態となった金属相があることを明らかにした。これにより磁束が量子凝縮した絶縁体を検証する準備が整った。
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