Control of electronic state in organic conductors by systematic band filling Original Research Article

Organic superconductors have been usually obtained by the bandwidth control of antiferromagnetic insulator. In order to find another parameter to control the electronic state, the band filling control has been applied to obtain the carrier-controlled organic conductors. As a result, the systematic band filling control for four kinds of organic conductors has been succeeded. The obtained crystals were (a) 2:1 salts, λ-ET2(GaCl41−)1−x(CoCl42−)x [ET=bis(ethylenedithio)tetrathiafulvalene], doping to the antiferromagnetic insulator, (b) 2:1 salts, δ′-ET2(GaCl4)1−x(CoCl4)x, doping to the non-magnetic insulator, (c) 3:1 salts, α-ET3(CoCl4)1−x(GaCl4)x(TCE), doping to the charge ordered salt, and (d) 3:2 salts, β′-ET3(CoCl4)2−x(GaCl4)x, doping to the half-filled band insulator. For both 2:1 salts, (a) and (b), the semiconducting behaviors have transferred to relatively conductive semiconducting ones by doping. The largest change of transport property is observed for (d) β′-phase from semiconducting behavior of parent material to metallic ones [β′-ET3(CoCl4)2−x(GaCl4)x (x=0.88, 0.66)] down to 140 and 100 K, respectively. These systematic band filling control suggests that the doping to the 1/2-filled band insulator is most effective.