engleski

The effects of disorder in semimetallic and charge-ordered α-(BEDT-TTF)2I3

The quest for exotic electronic orderings is driven by our ability to produce said states as cleanly as possible, in a tunable manner and preferably cheap. Organic conductors with reduced dimensionality offer all of these desirable properties as their rich phase diagrams are created by the competition between the tendency of electrons to delocalize and the pronounced interactions between charge, spin and lattice. We discuss here the organic charge-transfer salt α-(BEDT-TTF)2I3, a highly anisotropic material whose phase diagram features a number of intriguing quantum effects, most notably at ambient pressure it undergoes a metal-to-insulator transition into a charge-ordered (CO) state with CO-induced ferroelectricity. The electronic behavior in the CO phase and its exact microscopic underpinnings are however still under heated discussion. As an intriguing link to Mott-like spin-liquid systems from the same family of salts, the dielectric response and structural considerations point toward the important role of disorder. Here we show a detailed systematic study of the titular compound at ambient pressure above and below the CO phase transition, in particular of its dielectric properties both in-plane and out-of-plane, resistivity, Hall effect and magnetoresistance. In the high-temperature semimetallic phase, dominant inter-pocket scattering equalizes mobilities of the electrons and holes creating an almost temperature-independent conductivity as well as a low Hall effect. At low temperatures, within the insulating charge-ordered phase dc transport, magnetoresistance, as well as dielectric response show fingerprints of disorder whose origin is found in the anion layers tightly hydrogen-bonded to the conducting BEDT-TTF molecules.

BEDT-TTF, metal-insulator transition, charge order, ferroelectricity, dielectric spectroscopy, magnetotransport, semimetal, inter-pocket scattering, disorder

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