The Metallic State in Neutral Radical Conductors: Dimensionality, Pressure and Multiple Orbital Effects

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• 作者：Di Tian ; Stephen M. Winter ; Aaron Mailman ; Joanne W. L. Wong ; Wenjun Yong ; Hiroshi Yamaguchi ; Yating Jia ; John S. Tse ; Serge Desgreniers ; Richard A. Secco ; Stephen R. Julian ; Changqing Jin ; Masaki Mito ; Yasuo Ohishi ; Richard T. Oakley
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：November 11, 2015
• 年：2015
• 卷：137
• 期：44
• 页码：14136-14148
• 全文大小：918K
• ISSN：1520-5126

文摘

Pressure-induced changes in the solid-state structures and transport properties of three oxobenzene-bridged bisdithiazolyl radicals 2 (R = H, F, Ph) over the range 0鈥?5 GPa are described. All three materials experience compression of their 蟺-stacked architecture, be it (i) 1D ABABAB 蟺-stack (R = Ph), (ii) quasi-1D slipped 蟺-stack (R = H), or (iii) 2D brick-wall 蟺-stack (R = F). While R = H undergoes two structural phase transitions, neither of R = F, Ph display any phase change. All three radicals order as spin-canted antiferromagnets, but spin-canted ordering is lost at pressures <1.5 GPa. At room temperature, their electrical conductivity increases rapidly with pressure, and the thermal activation energy for conduction E_act is eliminated at pressures ranging from 鈭? GPa for R = F to 鈭?2 GPa for R = Ph, heralding formation of a highly correlated (or bad) metallic state. For R = F, H the pressure-induced Mott insulator to metal conversion has been tracked by measurements of optical conductivity at ambient temperature and electrical resistivity at low temperature. For R = F compression to 6.2 GPa leads to a quasiquadratic temperature dependence of the resistivity over the range 5鈥?00 K, consistent with formation of a 2D Fermi liquid state. DFT band structure calculations suggest that the ease of metallization of these radicals can be ascribed to their multiorbital character. Mixing and overlap of SOMO- and LUMO-based bands affords an increased kinetic energy stabilization of the metallic state relative to a single SOMO-based band system.