Anisotropic charge dynamics in the Quantum spin-liguid candidate Kappa -(BEDT-TTF) sub(2) Cu sub(2)(CN) sub(3)

• Published in: Physical review. B, Condensed matter and materials physics Vol. 90; no. 19
• Main Authors: Pinteric, M, Culo, M, Milat, O, Basletic, M, Korin-Hamzic, B, Tafra, E, Hamzic, A, Ivek, T, Peterseim, T, Miyagawa, K, Kanoda, K, Schlueter, J A, Dressel, M, Tomic, S
• Format: Journal Article
• Language: English
• Published: 15-11-2014
• Subjects: Anisotropy; Charge; Dielectric relaxation; Direct current; Dynamics; Electrical resistivity; Hall effect; Mathematical models; Planes
• EISSN: 1550-235X
• ISSN: 1098-0121

We have in detail characterized the anisotropic charge response of the dimer Mott insulator Kappa -(BEDT-TTF) sub(2) Cu sub(2)(CN) sub(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 relaxorlike 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.