Band Structure and Physical Properties of α-STF2I3: Dirac Electrons in Disordered Conduction Sheets

Crystals

Ryusei Doi¹  Toshio Naito¹ 

[1] Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan;

关键词: organic conductors;    charge-transfer complexes;    Dirac cones;    zero-gap semiconductors;    electrons with relativistic behavior;    disorder;   

DOI  :  10.3390/cryst10040270

来源: DOAJ

【 摘 要 】

The compound being investigated is an organic charge-transfer complex of the unsymmetrical donor STF with I₃ [STF = bis(ethylenedithio)diselenadithiafulvalene], which is isostructural with α-ET₂I₃ and α-BETS₂I₃ [ET = bis(ethylenedithio)tetrathiafulvalene, BETS = bis(ethylenedithio)tetraselenafulvalene]. According to recent studies, the calculated band structure should represent a zero-gap semiconductor at 1 bar that is similar to α-ET₂I₃ under high pressure (>15 kbar). Such materials have attracted extensive interest because the electrons at the Fermi level can be massless Dirac fermions (MDFs), with relativistic behaviors like those seen in graphene. In fact, α-STF₂I₃ exhibited nearly temperature-independent resistivity, ρ, (~100–300 K), a phenomenon that is widely observed in zero-gap semiconductors. The non-Arrhenius-type increase in ρ (<~100 K) was consistent with the characteristics of interacting MDFs. The paramagnetic susceptibility, χ, (2–300 K)—as well as the reflectivity, R and optical conductivity, σ, (25–300 K; 400–25,000 cm⁻¹)—were also almost temperature independent. Furthermore, σ was practically independent of wavenumber at ~6000–15,000 cm⁻¹. There was no structural transition based on X-ray studies (90–300 K). Considering all the electrical, magnetic, optical and structural properties of α-STF₂I₃ at 1 bar, it was concluded that the salt possesses a band structure characterized with Dirac cones, which was consistent with the calculation.

【 授权许可】

Unknown