Charge-Transfer Complex $\kappa$-(BEST)${}_2$Cu${}_2$(CN)${}_3$ Analogous to Organic Spin Liquid Candidate

Abstract

We report the structural, electrical, and magnetic properties of the organic conductor $\kappa$-(BEST)${}_2$Cu${}_2$(CN)${}_3$ (BEST: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as $\kappa$-BEST-CN), which is isostructural with the quantum spin liquid candidate $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$ (ET: bis(ethylenedithio)tetrathiafulvalene; abbreviated as $\kappa$-ET-CN). Resistivity measurements demonstrate that $\kappa$-BEST-CN exhibits semiconducting behavior, governed by the same conducting mechanism as $\kappa$-ET-CN. Under a pressure of ~0.1 GPa, $\kappa$-BEST-CN undergoes a superconducting transition with an onset temperature of ~4 K. From the comparison of the critical pressures of superconductivity between $\kappa$-ET-CN and $\kappa$-BEST-CN, $\kappa$-BEST-CN can be regarded as a chemically pressurized analogue of $\kappa$-ET-CN. Therefore, $\kappa$-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 $\kappa$-ET-CN. Furthermore, the spin susceptibility of $\kappa$-BEST-CN is slightly larger than that of $\kappa$-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.

15 pages, 9 figures

References in corpus (8)

• U(1) Gauge Theory of the Hubbard Model : Spin Liquid States and Possible Application to k-(BEDT-TTF)_2 Cu_2 (CN)_3
• Mott Transition from a Spin Liquid to a Fermi Liquid in the Spin-Frustrated Organic Conductor kappa-(ET)2Cu2(CN)3
• Novel Pauli-paramagnetic quantum phase in a Mott insulator
• Gapped magnetic ground state in quantum-spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$-Cu${}_2$(CN)${}_3$
• Anisotropic charge dynamics in the quantum spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$
• Rise and Fall of Landau's Quasiparticles While Approaching the Mott Transition
• Systematic Variations in the Charge-Glass-Forming Ability of Geometrically Frustrated $\theta$-(BEDT-TTF)${}_{2}X$ Organic Conductors
• Persistence of fermionic spin excitations through a genuine Mott transition in $\kappa$-type organics