title: Emergence of the Dirac Electron System in a Single-Component Molecular Conductor under High Pressure.
abstract: Single-component molecular conductors can provide a variety of electronic states. We demonstrate here that the Dirac electron system emerges in a single-component molecular conductor under high pressure. First-principles density functional theory calculations revealed that Dirac cones are formed in the single-component molecular conductor [Pd(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate), which shows temperature-independent resistivity (zero-gap behavior) at 12.6 GPa. The Dirac cone formation in [Pd(dddt)2] can be understood by a tight-binding model. The Dirac points originate from the HOMO and LUMO bands, each of which is associated with different molecular layers. Overlap of these two bands provides a closed intersection at the Fermi level (Fermi line) if there is no HOMO-LUMO coupling. Two-step HOMO-LUMO couplings remove the degeneracy on the Fermi line, resulting in gap formation. The Dirac cones emerge at the points where the Fermi line intersects with a line on which the HOMO-LUMO coupling is zero.
authors.affiliation: Condensed Molecular Materials Laboratory, RIKEN , Wako-shi, Saitama 351-0198, Japan.
authors.forename: Reizo
authors.identifier: 0000-0002-2606-4657
authors.initials: R
authors.lastname: Kato
authors.affiliation: Condensed Molecular Materials Laboratory, RIKEN , Wako-shi, Saitama 351-0198, Japan.
authors.forename: HengBo
authors.initials: H
authors.lastname: Cui
authors.affiliation: Condensed Molecular Materials Laboratory, RIKEN , Wako-shi, Saitama 351-0198, Japan.|International Center for Young Scientists (ICYS), National Institute for Materials Science , Tsukuba 305-0044, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Tsumuraya
authors.affiliation: International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science , Tsukuba 305-0044, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Miyazaki
authors.affiliation: Department of Physics, Nagoya University , Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Suzumura