High-Pressure Crystal Structure and Unusual Magnetoresistance of a Single-Component Molecular Conductor [Pd(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)

Abstract

A single-component molecular crystal [Pd(dddt)2] has been shown to exhibit almost temperature-independent resistivity under high pressure, leading theoretical studies to propose it as a three-dimensional (3D) Dirac electron system. To obtain more experimental information about the high-pressure electronic states, detailed resistivity measurements were performed, which show temperature-independent behavior at 13 GPa and then an upturn in the low temperature region at higher pressures. High-pressure single-crystal structure analysis was also performed for the first time, revealing the presence of pressure-induced structural disorder, which is possibly related to the changes in resistivity in the higher-pressure region. Calculations based on the disordered structure reveal that the Dirac cone state and semiconducting state coexist, indicating that the electronic state at high pressure is not a simple Dirac electron system as previously believed. Finally, the first measurements of magnetoresistance on [Pd(dddt)2] under high pressure are reported, revealing unusual behavior that seems to originate from the Dirac electron state.

Modern History of Organic Conductors: An Overview

“…Recently, an increasing number of new SCMCs, most of which containing Au(III)-dithiolene complexes, have been reported [729,. Furthermore, new SCMC materials have been recently found to possess unique electronic band structures called Dirac cones [869][870][871][872]875,876,878,[880][881][882], which will be discussed in the next section. Reproduced from (a) Ref.…”

Electric Transport of Nodal Line Semimetal in Single-Component Molecular Conductor

“…7, we compare the present theoretical results with those of the experiment. 10,40 The conductivity of a single crystal under quasi hydrostatic pressure was measured by the four-probe method using the DAC (Diamond Anvil Cell) technique. For the convenience of comparison, we show the resistivity ρ y (= 1/σ y ).…”

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.…”

“…Unlike SESs, they exhibit neither metallic nor nonmetallic behavior. Examples include temperature (T)-independent resistivity [29,30], wavenumber-independent optical conductivity [31,32], and the unprecedented behavior of magnetoresistance [9,[19][20][21]25]. Additionally, the wide variety of organic ZGCs based on finely controllable syntheses add an advantage for systematic studies.…”

“…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.…”