2018 Fiscal Year Final Research Report
Correlation between the Local Structure, Quantum Phenomena and Superconductivity in Layered BiS2 Superconductors
| Project/Area Number |
16K05454
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Tokyo Metropolitan University |
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Principal Investigator |
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| Research Collaborator |
AOKI Yuji 首都大学東京, 理学研究科, 教授
HIGASHINAKA Ryuji 首都大学東京, 理学研究科, 助教
SAGAYAMA Hajime 高エネルギー加速器機構, 准教授
SAGAYAMA Ryouko 高エネルギー加速器機構, 研究員
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | BiS2系層状超伝導体 / 純良単結晶 / 量子臨界的挙動 / 超伝導 / 構造相転移 / 超格子構造 |
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| Outline of Final Research Achievements |
BiS2-based superconductors are pseudo-2D materials consisting of alternating stacks of block layers, which possess rare-earth Ln ions, and BiS2 conducting layers. We have grown high-quality single crystals
of Ln(OF)BiS2 with controlled carrier doping for each rare-earth elements. By using these crystals, we studied the crystal structure, 4f-electron magnetism and electronic conductivity.
We have found some drastic change of crystal structure and development of superlattice structures in La-based system at low temperatures with increasing carrier doping. We also found that unconventional quantum critical behaviors (logT divergence in the specific heat) in Ce-based materials in a nonmetallic state and heavy-fermion behaviors in Nd-based materials. In the superconducting state, we have found anomalous behaviors of the upper critical field Hc2, i.e., largely enhanced Hc2 caused by the breaking of the local inversion symmetry at the BiS2 bilayers.
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| Free Research Field |
物性物理学
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| Academic Significance and Societal Importance of the Research Achievements |
BiS2系超伝導体は、2012年に首都大の水口等によって発見され、典型的な強相関電子系超伝導体の銅酸化物系や、鉄系超伝導体と類似した層状構造を持つ物質として注目された。本研究の成果からは、銅酸化物や鉄系のいくつかの系と同様に、超伝導発現と構造転移や磁性が密接に関わっている共通の現象が見出され、研究の当初から指摘されてきた単純な構造の類似性のみならず電子状態としての類似性を確認し、超伝導発現に関わる普遍的性質の一端を明らかにすることに成功したと言える。また、非従来型の量子臨界現象が２次元性の強い非金属相の磁性として観測され、新たな準２次元磁性層の物性研究課題を開拓した。
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