On Ambient-Pressure Superconductivity in Organic Conductors: Electrical Properties of (DMET)₂I₃, (DMET)₂I₂Br and (DMET)₂IBr₂

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We discovered superconductivity at ambient pressure in (DMET)₂I₃ at 0.47 K and in (DMET)₂IBr₂ at 0.59 K (midpoints), where DMET is (dimethyl(ethylenedithio)diselenadithiafulvalene), while in (DMET)₂I₂Br, superconductivity was not observed down to 0.5 K. In the DMET salts, those with smaller molar volume exhibit higher transition temperature, contrary to the BEDT–TTF salts. The effect of the disorder of the anion orientation on superconductivity is discussed.