Anisotropic charge dynamics in the quantum spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$

Abstract

We have in detail characterized the anisotropic charge response of the dimer Mott insulator $\kappa$-(BEDT-TTF)${}_2$\-Cu${}_2$(CN)${}_3$ by dc conductivity, Hall effect and dielectric spectroscopy. At room temperature the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity $\rho (T)$. Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also the relaxation levels off. The observed behavior bears features of relaxor-like ferroelectricity. Because heterogeneities impede its long-range development, only a weak tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.

14 pages, 13 figures

References in corpus (10)

• Spin Dynamics of the Spin-1/2 Kagome Lattice Antiferromagnet ZnCu_3(OH)_6Cl_2
• 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
• Emergence of inhomogeneous moments from spin liquid in the triangular-lattice Mott insulator $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$
• Absence of charge order in the dimerized κ-phase BEDT-TTF salts
• Critical behavior at Mott-Anderson transition: a TMT-DMFT perspective
• Power-law Conductivity inside the Mott gap: application to $\kappa -(BEDT-TTF{)}_{2}C{u}_2(CN{)}_3$
• Power-law dependence of the optical conductivity observed in the quantum spin-liquid compound κ-(BEDT-TTF)2Cu2(CN)3
• Insulator-metal transition on the triangular lattice
• X-ray Irradiation-induced Carrier Doping Effects in Organic Dimer-Mott Insulators

Cited by in corpus (8)

• Gapped magnetic ground state in quantum-spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$-Cu${}_2$(CN)${}_3$
• Molecular Quantum Materials: Electronic Phases and Charge Dynamics in Two-Dimensional Organic Solids
• Anions effects on the electronic structure and electrodynamic properties of the Mott insulator $\kappa$-(BEDT-TTF)${}_2$Ag${}_2$(CN)${}_3$
• Metal-Insulator Transition in the Dimerized Organic Conductor $\kappa$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Br
• Ingredients for Generalized Models of $\kappa$-Phase Organic Charge-Transfer Salts: A Review
• ESR studies on the spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$: anomalous response below $T=8$ K
• Resonant inelastic x-ray scattering probes the electron-phonon coupling in the spin-liquid kappa-(BEDT-TTF)2Cu2(CN)3
• Transition of a prestine Mott insulator to a correlated Fermi liquid: Pressure-dependent optical investigations of a quantum spin liquid