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Charge-Transfer Complex κ-(BEST)2Cu2(CN)3 Analogous to Organic Spin Liquid Candidate
Takuya Kobayashi1,2, Kent A Sakurai1, Shinji Michimura1
1Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
None:
We report the structural, electrical, and magnetic properties of the organic conductor κ-(BEST)2Cu2(CN)3 (BEST: bis(ethylenediseleno)-tetrathiafulvalene; abbreviated as κ-BEST-CN), which is isostructural with the quantum spin liquid candidate κ-(ET)2Cu2(CN)3 (ET: bis(ethylenedithio)tetrathiafulvalene; abbreviated as κ-ET-CN). Resistivity measurements demonstrate that κ-BEST-CN exhibits semiconducting behavior, governed by the same conducting mechanism as κ-ET-CN. Under a pressure of ∼0.1 GPa, κ-BEST-CN undergoes a superconducting transition with an onset temperature of ∼4 K. From the comparison of the critical pressures of superconductivity between κ-ET-CN and κ-BEST-CN, κ-BEST-CN can be regarded as a chemically pressurized analogue of κ-ET-CN. Therefore, κ-BEST-CN, in which only the effective pressure changes without altering the anion structure, is considered a valuable reference material for elucidating the enigmatic properties observed in κ-ET-CN. Furthermore, the spin susceptibility of κ-BEST-CN is slightly larger than that of κ-ET-CN and shows weaker temperature dependence, which cannot be explained by the localized spin model. This behavior clarifies the anomalous magnetic properties of a system with frustration near the Mott transition, serving to stimulate future theoretical research.
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