Effects of Electron Correlations and Chemical Pressures on Superconductivity of ${\beta }^{\prime \prime }$-type Organic Compounds

Abstract

We investigate low-temperature electronic states of the series of organic conductors ${\beta }^{\prime \prime }$-(BEDT-TTF)${}_4$[(H${}_3$O)M(C${}_2$O${}_4$)${}_3$]G, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene, and M and G represent trivalent metal ions and guest organic molecules, respectively. Our structural analyses reveal that the replacement of M and G give rise to systematic change in the cell parameters, especially in the $b$-axis length, which has positive correlation with the superconducting transition temperature $T_{\mathrm{c}}$. Analyses of temperature and magnetic field dependences of the electrical resistance including the Shubnikov-de Haas oscillations elucidates that the variation of charge disproportionation, effective mass and the number of itinerant carriers, can be systematically explained by the change of the $b$-axis length. The changes of the transfer integrals induced by stretching/compressing the $b$-axis are confirmed by the band calculation. We discuss that electron correlations in quarter-filled electronic bands lead to charge disproportionation and the possibility of a novel pairing mechanism of superconductivity mediated by charge degrees of freedom.

arXiv comment7 pages, 8 figures

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Cited by in corpus (1)

• Anisotropic Fully-Gapped Superconductivity Possibly Mediated by Charge Fluctuations in a Nondimeric Organic Complex