Competition between Charge Ordering and Superconductivity in Layered Organic Conductors $\alpha$-(BEDT-TTF)${}_{2}M$Hg(SCN)${}_4$ (M = K, NH${}_4$)

Abstract

While the optical properties of the superconducting salt $\alpha$-(BEDT-TTF)${}_2$NH${}_4$Hg(SCN)${}_4$ remain metallic down to 2 K, in the non-superconducting K-analog a pseudogap develops at frequencies of about 200 cm${}^{-1}$ for temperatures T < 200 K. Based on exact diagonalisation calculations on an extended Hubbard model at quarter-filling we argue that fluctuations associated with short range charge ordering are responsible for the observed low-frequency feature. The different ground states, including superconductivity, are a consequence of the proximity of these compounds to a quantum phase charge-ordering transition driven by the intermolecular Coulomb repulsion.

4 pages, 3 figures

References in corpus (6)

• Charge Ordering in Organic ET Compounds
• Superconductivity mediated by charge fluctuations in layered molecular crystals
• Charge ordering and antiferromagnetic exchange in layered molecular crystals of the theta type
• Metal-insulator transition and charge ordering in the extended Hubbard model at one-quarter filling
• Magnetic field - temperature phase diagram of the organic conductor alpha-(BEDT-TTF)2KHg(SCN)4
• Correlation gap in the optical spectra of the two-dimensional organic metal (BEDT-TTF)_4[Ni(dto)_2]

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