Development of Organic Superconductors by Reduction of Intermolecular Interaction

Tetrachalcogenafulvalene（TCF） donors are no longer essential to the production of organic superconductors， excluding fullerene superconductors。事实上，含有非TCF-的π-电子捐赠者BDA-TTP [其中含有双氟1，3-dithiol-2-ylidene（BDY）单元作为π-电子系统]和基于1，3-dithiol-2-ylidene（DT）的π-donor DODHT提供超导电盐。我们针对这些π捐助者的分子设计策略是基于以下要求的： （一）σ-键框架的扩展，（二）π-系统的缩小。这些要求是为了使内分子相互作用得到澄清，在实现超导电性中将是关键的。在补充其超导电性时，我们发现了BDA-TTP中SbF_6和FeCl_4盐的优异物理性质。β-（BDA-TTP）_2SbF_6已经证明拥有最有效的环球质量（12.4±1.1 m_e），但仍在有机超导体中找到。这一结果表明，电子-电子相互作用可能在BDA-TTP超导体中得到增强。β-（BDA-TTP）_2FeCl_4下的角相关和可变温度磁场（MR）测量显示了MR的突然下降。在κ-（BETS）_2FeBr_4和λ-（BETS）_2FeCl_4下，揭示了磁场诱导的超导电性。“Similar to the superconductors”-（DODHT）_2 X（X=AsF_6 and PF_6） at 16.5 kbar， the”-（DODHT）_2 BF_4·H_2 O hydrate was found to undergo an superconducting transition under an applied pressure of 15.5 kbar。三种DODHT超级导体的常见特征是它们都显示压力诱导行为的各种变体，包括绝缘（或半导体）、金属和超级导体相位。就这样，我们成功地找到了一个系列的非基于TCF的有机超级导体，具有明显的功能。

Tetrachalcogenafulvalene(TCF) donors are no longer essential to the production of organic superconductors, excluding fullerene superconductors. Indeed, the non-TCF-containing π-electron donor BDA-TTP [which contains the bis-fused 1,3-dithiol-2-ylidene(BDY) unit instead of the TCF unit as a π-electron system] and the 1,3-dithiol-2-ylidene (DT)-based π-donor DODHT do give superconducting salts. Our molecular design strategy for these π-donors is based on the following requirements : (i)the extension of the σ-bond framework and (ii)the reduction of the π-system. These requirements are thought to lead to a decrease of intermolecular interaction, which would be crucial in achieving superconductivity. In addition to their superconductivity, we have found the outstanding physical properties of the SbF_6 and FeCl_4 salt of BDA-TTP. β-(BDA-TTP)_2SbF_6 was proved to have the largest effective cyclotron mass (12.4±1.1 m_e) yet found in organic superconductors. This result indicates that the electron-electron interaction is probably enhanced in the BDA-TTP superconductor. Angular dependent and variable-temperature magnetoresistance(MR) measurement for β-(BDA-TTP)_2FeCl_4 under pressure showed an abrupt drop of MR. A similar anomaly in MR has been reported in κ-(BETS)_2FeBr_4 and λ-(BETS)_2FeCl_4, which exhibit magnetic-field-induced superconductivity. Similar to the superconductors β"-(DODHT)_2X (X=AsF_6 and PF_6) at 16.5 kbar, the β"-(DODHT)_2BF_4・H_2O hydrate was found to undergo an superconducting transition under an applied pressure of 15.5 kbar. The common noticeable feature of the three DODHT superconductors is that they all show a variety of pressure-induced conducting behaviors, including the insulating (or semiconducting), metallic, and superconducting phases. In this way, we succeeded in finding a series of non-TCF-based organic superconductors with notable features.