Emergence of the Dirac Electron System in a Single-Component Molecular Conductor under High Pressure

Kato, Reìzo; Cui, Hongchang; Tsumuraya, Takao; Miyazaki, Tsuyoshi; Suzumura, Yoshikazu

doi:10.1021/jacs.6b12187

Cited by 61 publications

(97 citation statements)

References 23 publications

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“…A single-component molecular conductor [Pd(dddt) 2 ] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) exhibits nearly massless Dirac electrons under high pressure, which has been shown by almost temperature independent electronic resistivity and performing theoretical * E-mail: suzumura@s.phys.nagoya-u.ac.jp structural optimization using first-principles calculations based on density functional theory (DFT). 24) Further, the nodal line with a loop of Dirac points has been analyzed using an extended Hückel calculation for the DFT optimized structure. 25) The formation of Dirac points originates from the multi-orbital nature, where the parity is different between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital).…”

Section: Introductionmentioning

confidence: 99%

“…However, the description of the the matrix element is insufficient to reproduce the quantitative behavior of all the Dirac cone on the nodal line. The direction of both 24) The most conducting axis is given by b being perpendicular to the a-c plane. There are four Pd(dddt) 2 molecules in the unit cell (the solid line), which consists of two layers shown by Layer 1 and Layer 2.…”

Section: Introductionmentioning

confidence: 99%

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Role of Velocity Field and Principal Axis of Tilted Dirac Cones in Effective Hamiltonian of Non-Coplanar Nodal Loop

et al. 2019

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Nodal line in single-component molecular conductor [Pd(dddt)2] with a half-filled band has been examined to elucidate properties of Dirac cone on the non-coplanar loop. The velocity of the tilted cone is evaluated at respective Dirac points on the nodal loop, which is obtained by our first-principles band structure calculations [J. Phys. Soc. Jpn. 87 113701 (2018)]. In the previous study, we proposed a new method to derive an effective Hamiltonian with a 2 × 2 matrix using two kinds of velocities of the Dirac cone on the nodal line, and the momentum dependence of the Dirac points are fully reproduced only at symmetric points. In this work, we show that our improved method well reproduces reasonable behavior of all the Dirac cones and a very small energy dispersion of 6 meV among the Dirac points on the nodal line, which originate from three-dimensionality of the electronic state. The variation of velocities along the nodal line are shown by using principal axes of the gap function between the conduction and valence bands. Further, the electronic states of the nodal line semimetal is examined by calculating the density of states close to the chemical potential using the effective Hamiltonian.1 J. Phys. Soc. Jpn.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Role of Velocity Field and Principal Axis of Tilted Dirac Cones in Effective Hamiltonian of Non-Coplanar Nodal Loop

et al. 2019

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“…As shown by the band calculation, the metallic phase induced by high pressure may be 3D Dirac semimetal, which has a topological surface state in the presence of spin-orbit coupling and inversion symmetry breaking [1,3]. The emergence of the Dirac semimetal has recently observed in a single-component molecular conductor under high pressures [43,44].…”

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Molecular diamond lattice antiferromagnet as a Dirac semimetal candidate

et al. 2019

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The ground state of a molecular diamond-lattice compound (ET)Ag 4 (CN) 5 is investigated by the magnetization and nuclear magnetic resonance spectroscopy. We found that the system exhibits antiferromagnetic long-range ordering with weak ferromagnetism at a high temperature of 102 K owing to the strong electron correlation. The spin susceptibility is well fitted into the diamond-lattice Heisenberg model with a nearest neighbor exchange coupling of 230 K, indicating the less frustrated interactions. The transition temperature elevates up to ∼195 K by applying pressure of 2 GPa, which records the highest temperature among organic molecular magnets. The first-principles band calculation suggests that the system is accessible to a three-dimensional topological semimetal with nodal Dirac lines, which has been extensively searched for a half-filling diamond lattice.A half-filling diamond lattice has been recently attracted great interests as an example of three-dimensional (3D) Dirac semimetal with the linearly-crossing band dispersion near the Fermi level [1-4] along with the appealing example including Na 3 Bi and Cd 3 As 2 [5,6]. The system can be a strong topological insulator in the presence of spin-orbit coupling as a 3D analogue to graphene [1]. Despite the popular crystal structure, the material with the half-filled band has been known only in a putative material BiO 2 [3]. In the counterpart insulating system, the frustrated local moment on the diamond lattice has been extensively studied as a spin liquid candidate [7][8][9]. A typical example is the magnetic spinel (AB 2 C 4 ) with the A site diamond lattice [10][11][12][13][14][15][16][17][18], where the properties of the disordered state are under intense debate. A (topological) Mott transition is expected to occur from a spin disordered phase to a Dirac semimetal phase by tuning the electron correlation [2,7].Organic molecular compounds have provided the platform for investigating the pressure-tuned Mott transition for the soft crystal. The well-studied Mott-Hubbard systems such as κ-(ET) 2 X and Z[Pd(dmit) 2 ] 2 possess a quasi-two-dimensional triangular lattice of the molecular dimer unit [19][20][21] owing to the anisotropic intermolecular interactions between planar molecules. Thus there are only a few example of 3D molecular compounds including the diamond lattice, except for the inorganic-organic hybrid system such as Li(TCNE) and Cu(DCNQI) 2 [22][23][24], and no example is known for the half-filling diamond lattice consisting of organic molecules. The material search for 3D molecular compounds would be important for giving high-temperature magnets and superconductors.We present here the molecular material (ET)Ag 4 (CN) 5 [25] as a prime example of the 3D diamond lattice. It possesses the extremely high-symmetry crystal structure of the orthorhombic Fddd lattice with the lattice constants: a = 13.215(9) Å, b = 19.4783(1) Å, and c = 19.6506(1) Å. Each monovalent ET molecule is surrounded by the honeycomb framework of the closed-shell polyanion [Ag 4 (C...

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“…Thus, the conductivity is one of the most fundamental phenomena and has been shown to have very peculiar behaviors in bulk systems of two molecular conductors 7,8 . One is the two-dimensional organic conductor [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene], in which a zero-gap state with a tilted Dirac cone was found using a tight-binding model 9,10 .…”

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confidence: 99%

“…Indeed, the resistivity observed in these conductors is almost constant with increasing temperature. In spite of the strong temperature dependence of the Hall coefficient 7 , the constant resistiv-ity has been regarded as evidence of the presence of a Dirac electron 8,15 .…”

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Role of acoustic phonons in exotic conductivity of two-dimensional Dirac electrons

Suzumura

Ogata

2018

Phys. Rev. B

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We examine the effect of acoustic phonon scattering on the conductivity of two-dimensional Dirac electrons. The temperature (T ) dependence of the conductivity (σ) is calculated using the electron Green's function with damping by both the impurity (Γ0) and phonon (Γ ph ). For zero or small doping, on which the present Rapid Communication focuses, σ(T ) increases and becomes almost constant due to the competition between the Dirac electrons and the phonon scattering. Such strange behavior of σ(T ) is ascribed to an exotic mechanism of phonon scattering, whose momentum space is strongly reduced in the presence of a Dirac cone. For large doping, σ decreases due to the interplay of the Fermi surface and the phonon. The unconventional T dependence of the resistivity ρ(= 1/σ) for small doping is compared with that of the experiment of Dirac electrons in an organic conductor.

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Emergence of the Dirac Electron System in a Single-Component Molecular Conductor under High Pressure

Cited by 61 publications

References 23 publications

Role of Velocity Field and Principal Axis of Tilted Dirac Cones in Effective Hamiltonian of Non-Coplanar Nodal Loop

Role of Velocity Field and Principal Axis of Tilted Dirac Cones in Effective Hamiltonian of Non-Coplanar Nodal Loop

Molecular diamond lattice antiferromagnet as a Dirac semimetal candidate

Role of acoustic phonons in exotic conductivity of two-dimensional Dirac electrons

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