General phase diagram and unconventional superconductivity of lambda-type organic superconductors

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K05427
• 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: Hokkaido University
• Principal Investigator: KAWAMOTO Atsushi 北海道大学, 理学研究院, 教授 (60251691)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 13C-NMR / 69,71Ga-NMR / SDW / 超伝導 / 強相関電子系

Outline of Final Research Achievements

Site-selective 13C-NMR is one of the best probes for investigating the microscopic electronic properties of an unconventional organic superconductor, lambda-(BETS)2GaCl4. We revealed the antiferromagnetic fluctuation at high temperature and crossover behavior to Fermi liquid state at low temperature. We also found the development of 1/T1T just above Tc. To reveal the origin of the development, we examined the insulator phase adjacent the superconducting phase and we found a SDW phase on the insulating salt of lambda-(BETS)2GaBr0.75Cl3.25 suggesting the development of 1/T1T is due to the SDW fluctuation and the possibility of the superconductivity intermediated by SDW fluctuations.
We also performed 69/71Ga NMR, which can directly detect charge properties. The behavior of 1/T1T at low temperature could be interpreted by magnetic fluctuation and the results supported the SDW fluctuation just above Tc.

Free Research Field

磁気共鳴、固体物理、分子化学

Academic Significance and Societal Importance of the Research Achievements

新奇超伝導相を持つλ-(BETS)2GaCl4が、d波超伝導、パウリ限界を超える上部臨界磁場の可能性や類縁体での磁場誘起超伝導など現代物理学のトピックスを数多く含む物質である。しかし、同様に詳細に研究されたκ型塩やTMTCF塩が、その近傍の電子状態を含む詳細な統一相図が提唱されているのに対して、この塩では、超伝導相に隣接する絶縁相の性質ですら解明されていない。超伝導の発現メカニズムを解明するうえで隣接絶縁相の情報は重要な知見を与える。本課題によるSDW相の発見は、λ-(BETS)2GaCl4の研究に謬ような知見をあたえるものである。