Electronic state of new type layered organic superconductors including strongly correlated insulating layers

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K05436
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Kawamoto Tadashi 東京工業大学, 物質理工学院, 助教 (60323789)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 超伝導 / 結晶構造 / 電荷秩序 / モット絶縁体

Outline of Final Research Achievements

The ground state of the genuine Mott insulator (BEDT-TTF)TaF6 is an antiferromagnetic insulating state below the Neel temperature 10 K. Structural and electronic states of organic conductors composed of (BEDT-TTF)2TaF6 have been investigated. The kappa-type compound is a dimer-Mott insulator, and has an anisotropic triangular lattice located between the triangular lattice and the one-dimensional limit. This compound shows a paramagnetic state down to 1.6 K, indicating the possibility if a spin liquid phase. The superconducting transition of the layered organic superconductor (EtDTET)(TCNQ) shows strongly sample dependences. The superconducting transition temperature has been measured by the magnetic torque, and the crystal structure of the same sample has been analyzed. The quantum oscillation of two polymorphs in (BEDT-TTF)2Cu(CF3)4(TCE) has been measured; the cross-sectional area of the Fermi surface indicates that the energy band of both compounds is effectively half-filled.

Free Research Field

有機伝導体

Academic Significance and Societal Importance of the Research Achievements

固体において、同一サイトでの電子のクーロン反発によって絶縁体となるモット絶縁体の研究は古くからなされている。四角格子をもつモット絶縁体はそれに相当する物質がないため、理論からの研究がなされている。(BEDT-TTF)TaF6は四角格子をもつ真性モット絶縁体であり、この物質の基底状態が反強磁性絶縁体であることを実験で確定させたことは、モット絶縁体の研究において重要な結果である。また、このような絶縁体の層が組み込まれた層状超伝導体の電子状態を実験により詳しく調べることで、超伝導発現における絶縁層の必要性の解明に繋がるものである。