Electric Transport of Nodal Line Semimetals in Single-Component Molecular Conductors

Abstract

We examine an effect of acoustic phonon scattering on the electric conductivity of a single-component molecular conductor [Pd(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) with a half-filled band by applying the previous calculation in a two-dimensional model with Dirac cone [Phys. Rev. B. 98, 161205 (2018)], wherethe electric transport by the impurity scattering exhibits a noticeable interplay of the Dirac cone and the phonon scattering, resulting in maximum of the conductivity with increasing temperature. The conductor shows a nodal line semimetal, where the band crossing of HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) provides a loop of Dirac points located close to the Fermi energy followed by the density of states (DOS) similar to that of a two-dimensional Dirac cone. Using a tight-binding (TB) model [arXiv:2008.09277], which was obtained using the crystal structure observed from a recent X ray diffraction experiment under pressure, it is shown that the obtained conductivity explains reasonably the anomalous behavior in [Pd(dddt)2] exhibiting temperature-independent resistivity at finite temperatures. This paper demonstrates a crucial role of the acoustic phonon scattering at finite temperatures in the electric conductivity of Dirac electrons. The present theoretical results of conductivity are compared with those of the experiments.

Anomalous conductivity of two-dimensional Dirac electrons in organic conductor under pressures

“…Taking a moderate magnitude of the e-p coupling constant, the almost T independent conductivity in the 2D plane has been obtained. 35) Finally, we compare our result with that of experiment. Temperature dependence of resistance (corresponding to the inverse of the conductivity) under hydrostatic pressures shows nearly constant behavior at high temperatures and a minimum at low temperatures, while the minimum is invisible for uniaxial pressure.…”

Donor-Type Nickel–Dithiolene Complexes Fused with Bulky Cycloalkane Substituents and Their Application in Molecular Conductors

“…However, the donors with cycloalkane substituents can adjust the proportions of the inter-and intra-dimer interactions through the S•••S contacts in their radical cation crystals by modification of the cycloalkane moieties, and allow for the realization of various cation radical crystals with unique donor arrangements by introducing linear, tetrahedral, and octahedral anions. Moreover, neutral crystals are potential candidates for new single-component molecular conductors [58][59][60][61][62][63].…”

“…A cation radical crystal, [Ni(dddt) 2 ] 3 (AuBr 2 ) 2 , is the first metal based on the donor-type metal-dithiolene complexes exhibiting metallic behavior down to at least 1.3 K [57]. Recently, Kato et al reported a single-component molecular Dirac electron system based on Pd(dddt) 2 that exhibits temperature-independent resistivity under high hydrostatic pressures [58][59][60][61][62][63]. The conducting and magnetic properties exhibited by the molecular crystals based on the dithiolene complexes are significantly dependent on the molecular arrangements of the metal-dithiolene complexes and organic molecular conductors.…”

New Organic Crystalline Material Close to Nodal-Line Materials: α′-STF2IBr2

“…Recently, the Dirac electron systems (DESs), or more generally topological materials (TMs), have been paid increasing attention [1][2][3][4][5][6][7][8]. In organic or molecular materials, the charge-transfer (CT) complexes/salts containing DESs called zero-gap conductors (ZGCs) have been intensively studied for nearly two decades [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. This is not only because of their unique physical properties, but also because of their advantage for research on basic electronic properties and the mechanism of production of DESs owing to the well-defined structures and stoichiometries.…”

“…Additionally, the wide variety of organic ZGCs based on finely controllable syntheses add an advantage for systematic studies. Since the discovery of the ZGC in organic compounds, α-ET 2 I 3 under high pressure (p > 12-15 kbar) (ET = bis(ethylenedithio)tetrathiafulvalene, Figure 1) [9], many kinds of molecular crystalline materials have also been reported to exhibit electronic properties and band structures characteristic to the ZGCs [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. In this way, our understanding of organic ZGCs has made substantial progress over the last 10-15 years, regarding band structures and electrical and magnetic properties.…”