title: The metallic state in neutral radical conductors: dimensionality, pressure and multiple orbital effects.
abstract: 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 0-15 GPa are described. All three materials experience compression of their π-stacked architecture, be it (i) 1D ABABAB π-stack (R = Ph), (ii) quasi-1D slipped π-stack (R = H), or (iii) 2D brick-wall π-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 Eact is eliminated at pressures ranging from ∼3 GPa for R = F to ∼12 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 5-300 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.
authors.affiliation: Department of Physics, University of Toronto , Toronto, Ontario M5S 1A7 Canada.
authors.forename: Di
authors.initials: D
authors.lastname: Tian
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Winter
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Aaron
authors.initials: A
authors.lastname: Mailman
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Joanne W L
authors.initials: JW
authors.lastname: Wong
authors.affiliation: Department of Earth Sciences, University of Western Ontario , London, Ontario N6A 5B7, Canada.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Yong
authors.affiliation: Faculty of Engineering, Kyushu Institute of Technology , Kitakyushu 804-8550, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamaguchi
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing, 100080, China.
authors.forename: Yating
authors.initials: Y
authors.lastname: Jia
authors.affiliation: Department of Physics, University of Saskatchewan , Saskatoon, Saskatchewan S7N 5E2, Canada.
authors.forename: John S
authors.initials: JS
authors.lastname: Tse
authors.affiliation: Department of Physics, University of Ottawa , Ottawa, Ontario K1N 6N5, Canada.
authors.forename: Serge
authors.initials: S
authors.lastname: Desgreniers
authors.affiliation: Department of Earth Sciences, University of Western Ontario , London, Ontario N6A 5B7, Canada.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Secco
authors.affiliation: Department of Physics, University of Toronto , Toronto, Ontario M5S 1A7 Canada.|Canadian Institute for Advanced Research , Toronto, Ontario M5G 1Z8, Canada.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Julian
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing, 100080, China.
authors.forename: Changqing
authors.initials: C
authors.lastname: Jin
authors.affiliation: Faculty of Engineering, Kyushu Institute of Technology , Kitakyushu 804-8550, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Mito
authors.affiliation: Materials Science Division, Japan Synchrotron Radiation Research Institute , SPring-8, Sayo, Hyogo 679-5198, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ohishi
authors.affiliation: Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Oakley